Perovskite catalysts and uses thereof

Abstract

The present disclosure provides perovskite catalytic materials and catalysts comprising platinum-group metals and perovskites. These catalysts may be used as oxygen storage materials with automotive applications, such as three-way catalysts. They are also useful for water or CO.sub.2 reduction, or thermochemical energy storage.

Claims

1. A three-way catalyst consisting essentially of a platinum-group metal and a perovskite having the formula CaCo.sub.1-xZr.sub.xO.sub.3-δ wherein x is a number defined by 0.02≤x≤0.98; and δ is a number defined by 0.0≤δ≤1.0.

2. The catalyst of claim 1, wherein the platinum-group metal is Pd, Pt, Rh, Ru or a combination thereof.

3. The catalyst of claim 1, wherein the platinum-group metal is a combination of Pd and Rh.

4. The catalyst of claim 1, wherein the catalyst is on an Al.sub.2O.sub.3 support, a titania support, a zirconia support, a ceria support, a silica support, an alumina-silica support, a zeolite support, or a carbon support.

5. The catalyst of claim 1, wherein the catalyst is formed into a monolith honeycomb block.

6. The catalyst of claim 1, wherein the catalyst is coated on to a ceramic monolith honeycomb block.

7. The catalyst of claim 6, wherein the ceramic monolith honeycomb block is a cordierite compound.

8. The catalyst of claim 1, wherein the catalyst is used to catalyze the reduction of NO.sub.x or the oxidation of CO or hydrocarbons from an internal combustion engine.

9. The catalyst of claim 8, wherein the internal combustion engine is an automobile engine.

10. The catalyst of claim 8, wherein the internal combustion engine is operated under stoichiometric air-to-fuel ratio conditions.

11. The catalyst of claim 8, wherein the internal combustion engine is fueled by diesel fuel, ethanol-gasoline hybrid fuel, gasoline or natural gas.

12. The catalyst of claim 11, wherein the ethanol-gasoline hybrid fuel is 85% ethanol 15% gasoline (E85).

13. A method for reducing emissions from an internal combustion engine which comprises contacting an exhaust stream from the internal combustion engine with a three-way catalyst comprising a platinum-group metal and a perovskite having the formula CaCo.sub.1-xZr.sub.xO.sub.3-δ wherein x is a number defined by 0.02≤x≤0.98; and δ is a number defined by 0.0≤δ≤1.0.

14. The method of claim 13, wherein the platinum-group metal is Pd, Pt, Rh, Ru or a mixture thereof.

15. An exhaust system for reducing emissions from an internal combustion engine which comprises the catalyst of claim 1.

16. A perovskite three-way catalyst having the formula CaCo.sub.1-xZr.sub.xO.sub.3-δ wherein x is a number defined by 0.02≤x≤0.98; and δ is a number defined by 0.0≤δ≤1.0.

17. The catalyst of claim 16 wherein x is a number defined by 0.2≤x≤0.8.

18. A method of preparing the perovskite three-way catalyst of claim 16, the method comprising: (a) dissolving salts of Ca, Co and Zr to form a homogenous gel; (b) drying the homogenous gel; and (c) calcining and sintering to form the perovskite three-way catalyst.

19. The method of claim 18, wherein the calcining is at about 300° C. to about 500° C. and the sintering is at about 800° C. to about 1400° C.

20. The method of claim 18, wherein step (a) further comprises first heating and dissolving salts of Ca, Co and Zr in citric acid and ethylene glycol to form a solution and second heating the solution to form a homogenous gel.

Description

4. BRIEF DESCRIPTION OF THE FIGURES

(1) FIGS. 1A-1B. X-ray diffraction (XRD) patterns of (FIG. 1A) state-of-the-art perovskite samples with different A- and B-site ions, (FIG. 1B) RTI's novel CaCo.sub.xZr.sub.1-xO.sub.3-δ perovskite samples with and without Pd doping.

(2) FIG. 2. Oxygen non-stoichiometry (δ) as a function of sample temperature of as-synthesized perovskite samples, in comparison with commercial CZO and CeO.sub.2. The result is calculated by using temperature programmed thermogravimetric (TG) data, assuming the onset temperature of thermal oxygen release is 500° C. (following complete sample degas).

(3) FIGS. 3A-3B. CO.sub.2 production and CO intake vs. reaction time on stream (TOS) and temperature of studied samples as represented by MS signals (in partial pressure) recorded during CO-TPR/MS measurements.

(4) FIG. 4. H.sub.2 consumption as a function of reaction time on stream and temperature of studied samples during H.sub.2-TPR measurements (temperature ramp rate at 5° C./min).

(5) FIGS. 5A-5B. CO.sub.2 production and 02 intake vs. reaction time on stream (TOS) of PE-1 to PE-6 perovskites, in comparison to CeO.sub.2 and CZO, as represented by MS partial pressure signals during isothermal CO reduction-Air oxidation cyclic tests at 500, 600, 700, and 800° C.

(6) FIG. 6. CO.sub.2 production and 02 intake vs. reaction time on stream (TOS) of PE-6 to 9 perovskite samples (CaCo.sub.xZr.sub.1-xO.sub.3-δ, with x=0.3, 0.5, 0.7, or 0.9), as represented by MS partial pressure signals during isothermal CO reduction-Air oxidation cyclic tests at 500, 600, 700, and 800° C.

(7) FIGS. 7A-7C. Plots for oxygen-intake kinetic calculation of CaCo.sub.0.5Zr.sub.0.5O.sub.3-δ perovskite sample showing (FIG. 7A) Fraction reacted α with time variation, (FIG. 7B) Fraction reacted a against reduced time t/t.sub.0.5, and (FIG. 7C) ln[−ln(1−a)] as a function of ln t (with t in min) for the determination of reaction mechanisms at temperatures varied from 350° C. to 475° C.

(8) FIG. 8. Temperature dependent-reaction rate constants k in natural log scale as a function of inverse temperature for the calculation of reaction activation energy for CaCo.sub.0.5Zr.sub.0.5O.sub.3-δ perovskite. The k value is achieved by fitting reaction data with various kinetic models, and first-order kinetic model was selected.

(9) FIG. 9. (1) CO and (2) C.sub.3H.sub.8 conversions during catalytic oxidation tests over (Panel 1a/2a) CaCo.sub.0.5Zr.sub.0.4Pd.sub.0.1O.sub.3-δ, (Panel 1b/2b) CaCo.sub.0.55Zr.sub.0.4Pd.sub.0.05O.sub.3-δ, and (Panel 1c/2c) CaCo.sub.0.5Zr.sub.0.5O.sub.3-δ perovskite with simulated exhaust feed at stoichiometric numbers (SNs) of 1.16, 1.07 and 0.95.

5. DETAILED DESCRIPTION OF THE DISCLOSURE

5.1. Definitions

(10) While the following terms are believed to be well understood by one of ordinary skill in the art, the following definitions are set forth to facilitate explanation of the presently disclosed subject matter.

(11) The term “oxygen storage material” (OSM) as used herein means a stable material that has the capacity to both reversibly take up with gas phase oxygen and release the oxygen. In one embodiment, such as automobile exhaust, OSMs may take up oxygen from NO.sub.x or release oxygen for the oxidation of hydrocarbons or carbon monoxide. The perovskite catalysts described herein are OSMs. The perovskite catalysts may be combined with conventional OSMs such as Ce.sub.xO.sub.y—ZrO.sub.2 (CZO) mixed oxides.

(12) The term “perovskite” means a metal oxide of the formula ABO.sub.3-a or A.sup.1A.sup.2B.sup.1B.sup.2O.sub.3-δ having a cubic crystalline form. The cations A and B are metals that may have multiple valence states, and are stable in both octahedral and dodecahedral environments.

(13) The term “platinum-group metal” or (PGM) means a group VIII metal from the periodic table. Preferred PGMs are Pd, Pt, Rh, Ru or combinations thereof.

(14) The term “three-way catalyst” or (TWC) means a substance that enables the oxidation of CO, unburnt hydrocarbons (HCs) or the reduction of NO.sub.x to N.sub.2 to proceed at a usually faster rate or at a lower temperature. The three chemical reactions may be simultaneous or may occur in a staged catalytic system such as the TWC systems disclosed in U.S. Pat. No. 7,718,562 where a first catalyst reduces the NO.sub.x and a second catalyst oxidizes the CO and HCs. In a staged catalytic system, the perovskites disclosed herein may be present as a component of either the first stage catalyst, the second stage catalyst, or both stage catalysts.

(15) Throughout the present specification, the terms “about” and/or “approximately” may be used in conjunction with numerical values and/or ranges. The term “about” is understood to mean those values near to a recited value. For example, “about 40 [units]” may mean within ±25% of 40 (e.g., from 30 to 50), within ±20%, ±15%, ±10%, ±9%, ±8%, ±7%, ±6%, ±5%, ±4%, ±3%, ±2%, ±1%, less than ±1%, or any other value or range of values therein or there below. Furthermore, the phrases “less than about [a value]” or “greater than about [a value]” should be understood in view of the definition of the term “about” provided herein. The terms “about” and “approximately” may be used interchangeably.

(16) Throughout the present specification, numerical ranges are provided for certain quantities. It is to be understood that these ranges comprise all subranges therein. Thus, the range “from 50 to 80” includes all possible ranges therein (e.g., 51-79, 52-78, 53-77, 54-76, 55-75, 60-70, etc.). Furthermore, all values within a given range may be an endpoint for the range encompassed thereby (e.g., the range 50-80 includes the ranges with endpoints such as 55-80, 50-75, etc.).

(17) As used herein, the verb “comprise” as is used in this description and in the claims and its conjugations are used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded.

(18) Throughout the specification the word “comprising,” or variations such as “comprises” or “comprising” will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. The present disclosure may suitably “comprise”, “consist of” or “consist essentially of”, the steps, elements, and/or reagents described in the claims.

(19) It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for use of such exclusive terminology as “solely”, “only” and the like in connection with the recitation of claim elements, or the use of a “negative” limitation.

(20) Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Preferred methods, devices, and materials are described, although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present disclosure. All references cited herein are incorporated by reference in their entirety.

(21) The following Examples further illustrate the disclosure and are not intended to limit the scope. In particular, it is to be understood that this disclosure is not limited to the particular embodiments described, which as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present disclosure will be limited only by the appended claims.

6. EXAMPLES

(22) The present study focuses on a systematic screening of advanced perovskites as potential substitutes for commercial CZO in TWC structure for automotive applications. Some perovskite compositions used for material synthesis were selected based on the most recent literature reporting profound material performances in other applications.sup.30-34. CaCo.sub.xZr.sub.1-xO.sub.3-δ perovskites were synthesized for the first time and reported here to show outstanding redox property and oxygen mobility compared to the current state-of the-art perovskite materials and the commercial CZO. CO— and H.sub.2-temperature programmed oxidation measurements, and dynamic CO-air redox cyclic tests were performed to examine the CO and oxygen storage capacities of the as-synthesized materials, in comparison with the commercial CZO and CeO.sub.2. Oxygen non-stoichiometry measurements were applied to study the correlation between temperature-dependent oxygen vacancy population and the material redox property. X-ray fluorescence, X-ray diffraction, and BET surface area measurements were used to characterize the studied materials. The kinetic data of the oxygen intake of the best performing perovskite materials is included. The study aims at providing a comprehensive comparison of the oxygen storage/release capacities of the current state-of-the-art perovskite materials, and preliminary results for the development of high performing perovskite materials in automotive and other potential applications.

2. EXPERIMENTAL

(23) 2.1. Perovskite Material Synthesis

(24) Perovskites with target compositions of CaCo.sub.xZr.sub.1-xO.sub.3-δ(x=0, 0.3, 0.5, 0.7 and 0.9) and Pd-doped CaCo.sub.0.6-yZr.sub.0.4Pd.sub.yO.sub.3-δ(y=0.05, 0.1 and 0.2) were synthesized using Pechini method..sup.35 Calcium nitrate tetrahydrate (Sigma-Aldrich, St. Louis, Mo.), cobalt (II) nitrate hexahydrate (STREM Chemical, Newburyport, Mass.), zirconium (IV) oxynitrate hydrate (Sigma-Aldrich) and palladium (II) nitrate dihydrate (Alfa Aesar, Tewksbury, Mass.) were used as the metal precursors. Stoichiometric amounts of metal nitrate salts were first dissolved in ethylene glycol (Acros Organics, Pittsburgh, Pa.), followed by the addition of citric acid (Fisher Chemical, Pittsburgh, Pa.), with input molar ratios of n(metal):n(citric acid):n(ethylene glycol)=2:3:9. A solution was formed at 150° C. and then was slowly heated to 250° C. under continuous stirring till a homogeneous gel was formed, which was then cooled to RT. Calcination was then performed at 400° C. for 4 hrs, followed by sintering at 1200° C. for 4 hrs in a high temperature oven with constant dry air flow (5 mL/min). Commercial Ce.sub.xO.sub.y—ZrO.sub.2 (CZO, with Ce:Zr molar ratio of 1:4) and CeO.sub.2 were respectively acquired from MEL Chemical (Flemington, N.J.) and Alfa Aesar. Other perovskites including La.sub.0.6Sr.sub.0.4CoO.sub.3-δ, Sr.sub.0.76Ca.sub.0.24FeO.sub.3-δ, LaCo.sub.0.6Ru.sub.0.4O.sub.3-δ, SrCo.sub.0.85Fe.sub.0.15O.sub.3-δ, and La.sub.0.5Ca.sub.0.5MnO.sub.3-δ were synthesized according to literature..sup.30-34

(25) 2.2. Oxygen Non-Stoichiometry Study

(26) The temperature-dependent oxygen non-stoichiometry (6) of the as-synthesized perovskites samples were studied by temperature programmed thermogravimetric analysis (TGA) using a TA Q500 unit. Around 20 mg sample was first loaded onto a platinum pan, and degassed at 500° C. for 2 hrs in He at a flow rate of 60 mL/min. The weight loss of the degassed sample was then measured with increasing temperature from 500° C. to 900° C. at ramp rate of 5° C./min in helium at the same flow rate. The oxygen non-stoichiometry was correlated to the sample weight loss, assuming 500° C. was the onset temperature of the thermal oxygen release. The imaginary oxygen non-stoichiometry of commercial Ce.sub.xO.sub.y—ZrO.sub.2 (CZO, with Ce:Zr molar ratio of 1:4, MEL Chemical) and CeO.sub.2 (Alfa Aesar) were also calculated in comparison with the studied perovskites. A background measurement with an empty platinum pan was performed with the same reaction program to take into account the buoyancy effect.

(27) 2.3. CO-Temperature Programmed Reduction Measurements

(28) CO-temperature programmed reduction (CO-TPR) measurements of the as-synthesized perovskite and commercial samples were performed using a Micromeritics AutoChem II 2920 reactor equipped with a built-in TCD detector, and with the reactor downstream connected to a benchtop quadrupole mass spectrometer (TA Discovery Mass Spectrometer). The TCD signal was used for the quantification of the CO intake, while the MS signal was used for product gas identification and semi-quantifiable analysis. Around 0.5 g sample sandwiched in thin quartz wool was first loaded into a U-shaped quartz reactor, which was housed in a thermal furnace with upper temperature limit of 1000° C. After degassing at 500° C. for 1 hr in He at a flow rate of 50 mL/min, the sample was heated from ambient temperature (25° C.) to 900° C. at 5° C./min in 20% CO/He, at a flow rate of 30 mL/min, while the TCD and MS responses were recorded every 0.1 second. The TCD calibration for the total signal (reduced CO and increased CO.sub.2 amount) was performed by using both the CO and CO.sub.2 linear calibration curves, and 20% CO/He was used as the reference gas. A background test with an empty reactor and the same reaction conditions was performed to create a baseline.

(29) 2.4. H.sub.2-Temperature programmed reduction measurements

(30) H.sub.2-temperature programmed reduction (H.sub.2-TPR) measurements of the as-synthesized perovskite and commercial samples were performed using the same above mentioned AutoChem reactor system. Around 0.5 g sample was first degassed at 500° C. for 1 hr in He at a flow rate of 50 mL/min, and then heated from ambient temperature (25° C.) to 900° C. at 5° C./min in 10% H.sub.2/Ar, at a flow rate of 30 mL/min. The water generated during TPR was trapped instantly downstream to the reactor by using a propanol-liquid N.sub.2 mixture coolant. The TCD calibration was performed with H.sub.2 concentrations varied from 0 to 10% in Ar, and with 10% H.sub.2/Ar as the reference gas. A background test with an empty reactor and the same reaction conditions was performed to create a baseline.

(31) 2.5. Dynamic Measurements of CO and Oxygen Storage Capacities

(32) The oxygen mobility within the studied samples were further examined using dynamic isothermal CO-air redox cyclic tests by using the same above mentioned AutoChem reactor system. Samples were first degassed in He (50 mL/min) at 500° C. for 2 hrs before cyclic tests. Each cycle was performed following the CO reduction-air oxidation order, respectively at 500° C., 600° C., 700° C., and 800° C., with 3 repetitive cycles at each reaction temperature. During the reduction, 20% CO/He flowed through the sample at a constant flow rate of 30 mL/min. During the oxidation, air (moisture removed) flowed through the sample at a constant flow rate of 30 mL/min. The reduction and oxidation durations were both kept at 0.5 min (30 sec). In between reduction and oxidation steps, He at a flow rate of 50 mL/min was used to purge the system residual gas. The CO.sub.2 production during the reduction cycles, and the O.sub.2 uptakes during the oxidation cycles were closely monitored by TCD and MS signals. A background test with an empty reactor was performed at the same cyclic conditions.

(33) 2.6. Isothermal Thermogravimetric Experiments for Reaction Kinetic Study

(34) The reaction kinetics of best performing perovskite was studied by isothermal TG experiments using a TA Q500 unit. Approximately 20 mg of each studied sample was degassed at 500° C. in He (at 50 mL/min) for 1 hr, followed by pre-reduction in 20% CO/He (at 30 mL/min) for 1 hr at the same temperature. The pretreated sample was then placed in a shallow platinum pan and was heated to a target temperature (350, 375, 400, 425, 450, 475, or 500° C.) in flowing He at 60 mL/min. The flow was then switched to 5% 02/He to gradually oxidize the sample after the target temperature was reached and a stable baseline was achieved, while the sample weight signal was recorded every 0.1 second during the whole process. A background measurement with empty platinum pan was performed at each reaction temperature to take into account the buoyancy effect. The kinetic models were adopted from Hancock's [29] and Motohashi's [30] previous studies, with major calculation equations described accompanying the corresponding body text.

(35) 2.7. Catalyst Characterization

(36) 2.7.1. X-Ray Fluorescence (XRF) Analysis

(37) X-ray fluorescence analyses (XRF) for elemental compositional study of the studied materials were performed with ARL Thermo Scientific PERFORMX Wavelength-Dispersive X-ray Fluorescence (WDXRF) instrument. A 5GN-type Rh target incident beam with ultra-thin 30 μm Be window was used to maximize light element response. The instrument was equipped with two detectors and seven analyzer crystals to achieve a broad elemental range. Sample data was processed using UniQuant, a standard software package that uses advanced fundamental parameters algorithms to determine elemental concentrations. Analysis is for seventy-nine elements and those elements above ten times the instrument calculated uncertainty are reported.

(38) 2.7.2. X-Ray Diffraction (XRD) Analysis

(39) The phase identification was done by means of X-ray diffraction (XRD) analyses of the studied materials with a Thermo INEL Equinox 100 benchtop X-ray diffractometer. XRD patterns were collected with monochromatized Cu Kα radiation over the 2θrange of 20−70° with a total scanning duration of 1200 seconds at an instrument power setting of 40 kV and 0.9 mA. The scans were performed in validation of the instrument using the vendors Y.sub.2O.sub.3 standard yielded peak accuracy as compared to ICDD PDF reference values that fell well within the SOP-stated acceptable values of 0.05° of 2θ. All measurements were processed using Jade software.

(40) 2.7.3. BET Surface Area Analysis

(41) BET surface areas of the studied materials were measured using an ASAP 2020 Plus Chemisorption unit. Each sample (around 0.2 g) was first degassed in vacuum (<500 μm Hg) at 350° C. for 4 hrs. The Multi-point BET surface area of the degassed sample was measured under partial pressure P/P.sub.0 of 0.05 to 0.30 at liquid nitrogen temperature (77 K).

3. RESULTS AND DISCUSSION

(42) 3.1. Structural Analysis of Studied Materials

(43) The actual compositions of the as-synthesized perovskite samples were analyzed by XRF with replicate results within an error limit of <10%. The target (theoretical) and actual compositions of the studied materials are listed in Table 1. The differences between the two values for all perovskites are within allowable ranges. The analytical information of the commercial Ce.sub.xO.sub.y—ZrO.sub.2 (CZO) and CeO.sub.2 are provided by their manufactures. Table 1 also lists the tolerance factors (t) of the perovskites, calculated based on the theoretical material compositions. The t values were calculated based on the ionic radii of Ca.sup.2+, La.sup.3+, Sr.sup.2+ for A-site ions, and Co.sup.3+, Fe.sup.3+, Mn.sup.3+, Ru.sup.3+, Zr.sup.4+, and Pd.sup.2+ for B-site ions. The t values of PE-1 to 9 samples are within the range of 0.8˜0.92, suggesting stable orthorhombic perovskite structures..sup.3

(44) TABLE-US-00001 TABLE 1 Analytical data of as-synthesized ABO.sub.3-δ perovskite samples, and commercial Ce.sub.xO.sub.y—ZrO.sub.2 (CZO) and CeO.sub.2 samples. # Target composition Actual composition.sup.a t.sup.b Ā (m.sup.2/g).sup.c PE-1 La.sub.0.6Sr.sub.0.4CoO.sub.3-δ La.sub.0.56Sr.sub.0.47Co.sub.1.03O.sub.3-δ 0.91 1.16 PE-2 Sr.sub.0.76Ca.sub.0.24FeO.sub.3-δ Sr.sub.0.84Ca.sub.0.21Fe.sub.0.96O.sub.3-δ 0.92 2.36 PE-3 LaCo.sub.0.6Ru.sub.0.4O.sub.3-δ La.sub.0.99Co.sub.0.49Ru.sub.0.44O.sub.3-δ 0.86 2.58 PE-4 SrCo.sub.0.85Fe.sub.0.15O.sub.3-δ Sr.sub.1.10Co.sub.0.82Fe.sub.0.14O.sub.3-δ 0.94 2.59 PE-5 La.sub.0.5Ca.sub.0.5MnO.sub.3-δ La.sub.0.50Ca.sub.0.52Mn.sub.1.08O.sub.3-δ 0.89 2.09 PE-6 CaCo.sub.0.3Zr.sub.0.7O.sub.3-δ Ca.sub.1.33Co.sub.0.37Zr.sub.0.52O.sub.3-δ 0.82 1.88 PE-7 CaCo.sub.0.5Zr.sub.0.5O.sub.3-δ Ca.sub.1.17Co.sub.0.61Zr.sub.0.36O.sub.3-δ 0.84 3.19 PE-8 CaCo.sub.0.7Zr.sub.0.3O.sub.3-δ Ca.sub.1.12Co.sub.0.79Zr.sub.0.20O.sub.3-δ 0.85 2.21 PE-9 CaCo.sub.0.9Zr.sub.0.1O.sub.3-δ Ca.sub.1.08Co.sub.0.98Zr.sub.0.07O.sub.3-δ 0.86 1.76 PE-10 CaCo.sub.0.4Zr.sub.0.4Pd.sub.0.2O.sub.3 Ca.sub.1.12Co.sub.0.0.43Zr.sub.0.33Pd.sub.0.25O.sub.3 0.82 0.05 PE-11 CaCo.sub.0.5Zr.sub.0.4Pd.sub.0.1O.sub.3 Ca.sub.1.12Co.sub.0.55Zr.sub.0.32Pd.sub.0.11O.sub.3 0.83 0.03 PE-12 CaCo.sub.0.55Zr.sub.0.4Pd.sub.0.05O.sub.3 Ca.sub.1.16Co.sub.0.61Zr.sub.0.32Pd.sub.0.06O.sub.3 0.84 0.15 CZO.sup.d Ce:Zr molar ratio 1:4 Ce:Zr molar ratio 1:4 N/A 215.80 CeO.sub.2.sup.e CeO.sub.2 CeO.sub.2 N/A 15.52 Annotations: .sup.aMaterial actual composition as measured by XRF, with repeatable results and acceptance limits of less than 10%; .sup.bTheoretical tolerance factor (in the range of 0.75 to 1) for the perovskite material sample calculated based on the target compositions; .sup.cMulti-point specific BET surface areas Ā measured at liquid N.sub.2 temperature (77 K), at relative pressures (P/P.sub.0) in the range of 0.05 to 0.30; .sup.dCommercial CZO sample acquired from MEL Chemical, with material composition information provided; .sup.eCommercial CeO.sub.2 sample acquired from Alfa Aesar, with material composition information provided.

(45) More detailed material structural information of the studied materials can be obtained from XRD analyses. FIGS. 1A-1B plots the highly resolved XRD patterns of all the fresh samples. FIG. 1A presents the XRD patterns of as-synthesized perovskite samples PE-1 to 5 with different A- and B-site ions. The XRD pattern for La.sub.0.6Sr.sub.0.4CoO.sub.3-δ (PE-1) is consistent with database (PDF #01-070-7597) and previous report.sup.30, and is characteristic of the rhombohedral lattice structure. All the diffraction peaks for Sr.sub.0.76Ca.sub.0.24FeO.sub.3-δ (PE-2) can be assigned to perovskite-type structure (PDF #01-082-2445).sup.31. The diffraction pattern of the LaCo.sub.0.6Ru.sub.0.4O.sub.3-δ sample (PE-3) show profiles corresponding to single perovskite structures (PDF #01-082-9769) without peaks attributable to ruthenium oxides.sup.32. The XRD pattern of SrCo.sub.0.85Fe.sub.0.15O.sub.3-δ sample (PE-4) also agrees well with the previously reported perovskite structure without any impurity phases (PDF #04-014-2297).sup.33. La.sub.0.5Ca.sub.0.5MnO.sub.3-δ, (PE-5) showed distinct peaks which correspond well to previously reported La.sub.0.67Ca.sub.0.33MnO.sub.3 perovskite (PDF #04-014-6391).

(46) The XRD patterns of the PE 6-12 novel perovskite samples with or without Pd doping are shown in FIG. 1B. Reflections at 20 of 22.1, 31.0, 31.5, 32.0, 45.2, 50.2, 50.9, 51.6, 55.2, 55.9, 56.5, 56.7, 64.7, 65.8 and 66.9 were assigned to the main phase of orthorhombic Lakargiite CaZrO.sub.3 perovskite matrix (JCPDS 01-080-6213); reflections at 20 of 30.3, 35.1, 50.5, 60.0 and 63.0 were assigned to cubic Tazheranite ZrO.sub.2 structure (JCPDS 04-002-8314); reflections at 20 of 19.5, 32.5, 34.2, 41.6, 42.3, 46.4 and 47.8 were assigned to Ca.sub.3Co.sub.2O.sub.6 phase (JCPDS 04-010-0812); and reflections at 20 of 40.2 and 46.7 were assigned to Pd phase (JCPDS 01-089-4897).

(47) For CaCo.sub.xZr.sub.1-xO.sub.3 samples, with lower x values (higher Zr/Co ratio at B sites), higher perovskite main phase crystallinity was observed, while increased amount of ZrO.sub.2 phase was detected. When x>0.7, notable amount of Ca.sub.3Co.sub.2O.sub.6 phase was detected. This suggests that partial substitution of Co by Zr enhances the structural crystallinity of CaCoO.sub.3. With x value of around 0.5, CaCo.sub.0.5Zr.sub.0.5O.sub.3 processes optimum crystallinity and minimized impurity. Noteworthy, no side phases of Cobalt Oxides in any single form were identified when x<0.7, suggesting the Co was inside the perovskite unit cells.

(48) For CaCo.sub.0.6-yZr.sub.0.4Pd.sub.yO.sub.3 samples, the main phase remained CaCo.sub.xZr.sub.1-xO.sub.3 perovskite, as the characteristic peaks matched those observed with CaCo.sub.0.5Zr0.5O3. Peaks characterizing Pd were observed, and the Pd phase amount increased with increasing Pd loading. No peak corresponding to PdO was shown. This suggests that among the doped Pd, some were incorporated into the perovskite bulk crystal structure (bulk Pd.sup.2+), while others remained on the crystal surfaces (surface Pd.sup.0). The existence of bulk Pd.sup.2+ will be further evidenced by H.sub.2-TPR result in the following text.

(49) 3.2. Temperature-Dependent Oxygen Non-Stoichiometry of as-Synthesized Perovskites

(50) The temperature-dependent oxygen non-stoichiometry (5) of the as-synthesized perovskites and the commercial CeO.sub.2 and CZO samples are compared in the temperature range of 500° C. to 900° C. in FIG. 2. Generally, 6 values increase with increasing temperature. Remarkable differences in the δ increase rate are observed between perovskite and Ce-containing non-perovskite samples. Compared to perovskite samples, CeO.sub.2 and CZO showed negligible variations in δ values with temperature. Among perovskite samples, PE-1 to 5 showed steady 6 increase rate during the entire temperature programmed process, where PE-1 (La.sub.0.6Sr.sub.0.4CoO.sub.3-δ) was the leading material. Compared to PE-1 to 5, the oxygen release of CaCo.sub.xZr.sub.1-xO.sub.3-δ— type perovskites was a more thermally activated process, with δ values observed to increase exponentially at 780° C. Specifically, pronounced amount of oxygen vacancies were created in CaCo.sub.xZr.sub.1-xO.sub.3-δ when x>0.3 when temperature reached 800˜900° C.

(51) 3.3. Reducibility of as-Synthesized Perovskites in Comparison to Commercial Ceria-Based OSM

(52) CO-TPR/MS profiles of the as-synthesized perovskites and commercial ceria-based oxygen storage material (OSM) samples are presented by FIG. 3. No oxidation pretreatment was performed considering that the fresh samples as they were already exposed to oxidative calcination environments during material synthesis, i.e. 1200° C. in air for perovskite samples and around 550° C. in air for commercial CeO.sub.2 and CZO samples. Complete sample degas pretreatments were applied prior to all the measurements. FIGS. 3A-3B plots the semi-quantitative MS signals, in terms of partial pressure (in Torr) of the mass fraction, of respectively (FIG. 3A) CO.sub.2 (mass of 44) and (FIG. 3B) CO (mass of 28) in the CO-TPR product stream. The CO.sub.2 and CO baselines achieved by flowing the same reactant gas (10% CO/He) through an empty reactor tube at the same temperature conditions are also plotted. The positive CO.sub.2 peaks and negative CO peaks compared to baseline indicate sample reduction by CO as reduction temperature ramps from ambient to as high as 900° C. Higher extent of sample reduction is represented by higher intensity of CO.sub.2 signal and higher absolute value of the CO intensity.

(53) In FIGS. 3A-3B, highly resolved MS signals of CO.sub.2 and CO recorded during CO-TPR measurements suggest the efficacy of the analysis approach. The onset reduction temperatures of the studied samples were around 150° C. to 250° C., and the reduction extends as temperature increases to 900° C. For each sample, the outstanding TPR peaks at different temperature ranges represent varied types of solid reductions. For the perovskites, the reduction mainly occurred with the B cations (Co.sup.m+, Fe.sup.n+, Mn.sup.P+, and Ru.sup.q+) since all the A cations (Ca.sup.2+, La.sup.3+ and Sr.sup.2+) are non-reducible .sup.3 at the described conditions. More specifically, the reduction happened with the surface oxygen-stabilized B site ions. An exception was with CaCo.sub.xZr.sub.1-xO.sub.3-δ perovskite samples (PE-6 to 9), in which B site Zr.sup.4+ ions were non-reducible at the described conditions, while the incorporation of Zr.sup.4+ was simply for structural tuning reason as previously discussed.

(54) Generally, the volumetric amounts of CO consumptions (V.sub.CO, mL/g sample) follow the trend of CaCo.sub.xZr.sub.1-xO.sub.3-δ(x=0.9, 0.7, and 0.5)>LaCo.sub.0.6Ru.sub.0.4O.sub.3-δ>CaCo.sub.0.3Zr.sub.0.7O.sub.3-δ>La.sub.0.6Sr.sub.0.4CoO.sub.3-δ>La.sub.0.5Ca.sub.0.5MnO.sub.3-δ>CeO.sub.2>CZO>SrCo.sub.0.85Fe.sub.0.15O.sub.3-δ>Sr.sub.0.76Ca.sub.0.24FeO.sub.3-δ. The reducibility of all the as-synthesized perovskite samples are higher than the commercial CeO.sub.2 and CZO samples. Among the studied perovskites, CaCo.sub.xZr.sub.1-xO.sub.3-δ exhibits good reducibility in CO-TPR. Specifically, CaCo.sub.0.9Zr.sub.0.1O.sub.3-δ shows significantly enhanced reducibility than the current state-of-the-art La.sub.0.6Sr.sub.0.4CoO.sub.3-δ.

(55) FIG. 4 presents the H.sub.2— TPR profiles of CaCo.sub.xZr.sub.1-xO.sub.3 and CaCo.sub.0.6-yZr.sub.0.4Pd.sub.yO.sub.3. The TPR profiles of CaCo.sub.xZr.sub.1-xO.sub.3 (except for CaZrO.sub.3) show two successive reduction peaks, with one in the range of 280-500° C., and the other in the range of 450-680° C. Consistent with previous studies, the two peaks can be respectively assigned to the reduction of Co.sup.3+ to Co.sup.2+, and Co.sup.2+ to Co.sup.0,36,37 The amount of reducible sites increased with increasing Co contents. CaZrO.sub.3 showed no reduction at all, which further proved that the reductions occurred solely on the Co sites. On the other hand, the reduction temperatures for both peaks shift to lower values with increasing Zr content. This result indicates that B-site substitution with Zr enhanced the reduction of Co species by lowering the reduction temperature.

(56) The H.sub.2-TPR profiles of fresh Pd-doped samples CaCo.sub.0.6-yZr.sub.0.4Pd.sub.yO.sub.3-δ show obvious shifts of the high-temperature Co reduction peak (Co.sup.3+ to Co.sup.2+) to lower temperature (80-100° C. lower). Noticeable shifts to lower temperature of the Co.sup.2+-to-Co.sup.0 reduction peaks were also observed with Pd-doping. Moreover, the shifts were more significant with increasing Pd content. With the highest amount of Pd loading, three overlapping peaks are seen with CaCo.sub.0.4Zr.sub.0.4Pd.sub.0.2O.sub.3. The successive two reduction peaks at higher temperatures (T.sub.max=390° C. and 420° C.) can be assigned to Co reductions as discussed, while the lower temperature (T.sub.max=320° C.) peak corresponds to the reduction of oxide form of Pd (Pd.sup.2+) into Pd.sup.0.36 The peak area reduces with decreasing Pd content. Consistent with previous reports, this suggests that Pd facilitated the Co reduction and improved the catalyst reducibility, which may be attributed to the hydrogen dissociation on surface Pd.sup.0 particles followed by the successive spill-over of dissociated hydrogen atoms to the Co species..sup.38

(57) Both Pd-doped and un-doped perovskites showed higher reducibility than the CeO.sub.2 and CeO.sub.2—ZrO.sub.2 (CZO) samples. For CeO.sub.2, the main reduction happened at much higher temperature starting at 500° C., with T.sub.max at around 800° C., which is assigned to Ce.sup.4+ to Ce.sup.3+ reduction..sup.39 The incorporation of Zr.sup.4+ in CZO structure enhanced the reducibility of Ce species, with the reduction peak shifting to lower temperature (T.sub.max=520° C.). It is well established that in mixed ceria-zirconia a smaller ionic radius of zirconium favors the presence of Ce.sup.3+ ions by eliminating the strain associated with their formation, while the enhanced oxygen defects account for the improved reducibility/OSC..sup.40

(58) 3.4. Dynamic CO and Oxygen Storage Capacities for the Studied Materials

(59) The CO and oxygen storage capacities of the studied materials were measured by dynamic isothermal redox cyclic tests, where CO and O.sub.2 were respectively used as the reducing and oxidizing agents. During the measurement, constant flows of 20% CO/He and air were purged for transient periods (30 seconds) in sequence through the degassed sample, and He was purged (for 15 min) in between the reduction and oxidation steps to purge out the residual gas. The performance of each sample was studied isothermally at four redox temperatures (500, 600, 700, and 800° C.), while three repetitive measurements were performed in succession at each temperature. The gas product composition downstream were closely monitored by TCD and MS. FIGS. 5A-5B and FIG. 6 illustrate the MS responses (in terms of mass fraction partial pressure) of product CO.sub.2 (solid line peaks***) and unreacted O.sub.2 (dotted line peaks***) during the measurements for all the studied materials. Specifically, FIGS. 5A-5B compares the material performances among different types of perovskites (PE-1 to 6) and the commercial OSMs (CeO.sub.2 and CZO), while FIG. 6 presents the OSCs of CaCo.sub.xZr.sub.1-xO.sub.3-δ perovskites (PE-6 to 9) with varying x values. Appreciable CO.sub.2 formations (CO conversions) were detected at the studied temperatures for all studied materials during reduction. Generally, the redox properties increase with increasing temperature from 500° C. to 800° C. In addition, the isothermal process showed relatively steady responses for the CO conversion in the reduction steps and the O.sub.2 storage in the subsequent oxidation steps, suggesting stable material performance.

(60) In FIG. 6, the material redox properties improved with increasing temperature from 500° C. to 800° C., and with increasing x values (higher Co content). At lower temperatures (500° C. and 600° C.), repeatable redox behaviours were shown with all studied materials, indicating stable OSC performance. As redox temperature was elevated (800° C.), CaCo.sub.xZr.sub.1-xO.sub.3-δ (when x>0.5) showed profound CO consumption during reduction, but continuously decreasing O.sub.2 consumption during oxidation with cycles. This was likely due to the instability of Co (CoO phase was released from the main phase through decomposition) at high temperature reducing atmosphere..sup.41 When higher amount of Zr was present in the perovskites (x≤0.5), the oxygen storage was repeatable even at higher temperatures. This is consistent with the previously stated hypothesis that stabilized CaCo.sub.xZr.sub.1-xO.sub.3-δ perovskite structures can be achieved by partial substitution of B-site Co with certain amount of Zr (x≤0.5). When x=0.5, the optimum perovskite composition CaCo.sub.0.5Zr.sub.0.5O.sub.3-δ exhibited optimum oxygen storage capacity and stability.

(61) 3.5. Reaction Kinetic Study of Oxygen-Intake of CaCo.sub.0.5Zr.sub.0.5O.sub.3-δ

(62) The oxygen intake kinetics of reduced CaCo.sub.0.5Zr.sub.0.5O.sub.3-δ perovskite were further studied. FIGS. 7A-7C shows plots used for kinetic calculation based on isothermal TG data between 350 and 475° C., and under 5% O.sub.2/He. Prior to measurement at each temperature, the sample was completely degassed at 500° C. and pre-reduced by 10% CO/He at the same temperature. The data are analysed based on the solid-state kinetic study methodology summarized by Hancock and Sharp,.sup.42 and recent related discussions by Motohashi, et al..sup.43 The time-dependent fraction of the solid reacted (α) and its variation (ln[−ln(1−α)]) are plotted as a function of time on stream (t), reduced time t/t.sub.0.5, or time in log scale (ln t). The fraction reacted (α) is calculated using Eq. (4), where m.sub.0, m.sub.t, and m.sub.final are respectively the sample weight at the beginning, time on stream of t (in min), and the end of TG measurement during sample oxidation. A scale of 0-1 is allowed for the α value, with α=0 and α=1 respectively indicating the onset and the equilibrium states of the solid reaction.

(63) $\begin{array}{cc}\alpha =\frac{m_0-m_t}{m_0-m_{\mathrm{final}}}& \left(4\right)\end{array}$

(64) Generally, sample oxidation rate accelerates with increasing temperature from 350° C. to 475° C. (FIG. 7A), and decreases with increasing time on stream by showing a smaller slope as t/t.sub.0.5 value increases for each curve (FIG. 7B). The reaction mechanisms can be examined by plotting ln[−ln(1−α)] as a function of ln t (with t in min) when a linear rate-rated equation with slope m is acquired (FIG. 7C). The m values of all the linear curves fall in the range of 0.6-1.3 (m=1.29, 1.23, 1.31, 1.09, 0.88, 0.61 respectively at 350, 375, 400, 425, 450 and 475° C.).

(65) The data points at 350° C.≤T≤475° C. nicely obey rate equation Eq. (5), indicating first-order kinetics for both samples at the studied oxidation reaction conditions. Following Arrhenius equation, the reaction rate constants (k) in log scale upon oxygen intakes were then plotted against inverse temperature (1000/T), as shown as FIG. 8. The reaction activation energy (E.sub.A, in eV) values for the oxygen intake process was calculated to be 0.159 eV for CaCo.sub.0.5Zr.sub.0.5O.sub.3-δ perovskite.
−ln(1−α)=kt  (5)

(66) 3.6. Catalytic CO and HC Oxidation Activities of Pd-Doped CaCo.sub.xZr.sub.1-xO.sub.3-δ

(67) Catalytic activities for CO and HC oxidation at simulated exhaust feed with Pd-doped CaCo.sub.0.6-yZr.sub.0.4Pd.sub.yO.sub.3-δ(y=0, 0.05 and 0.1) perovskite samples were investigated. C.sub.3H.sub.6 was used as the model compound for HC. FIG. 9 presents the catalytic oxidation activity of fresh (a) CaCo.sub.0.5Zr.sub.0.4Pd.sub.0.1O.sub.3-δ, (b) CaCo.sub.0.55Zr.sub.0.4Pd.sub.0.05O.sub.3-δ and (c) CaCo.sub.0.5Zr.sub.0.5O.sub.3-δ, with corresponding dopant Pd contents (wt-%) of 5.0%, 2.5% and 0%. The oxidation activities were profiled as CO and C.sub.3H.sub.8 conversions vs. reaction temperature from 150-550° C., every 25° C. The conversion profiles were collected at three different stoichiometric numbers (SNs) at 0.95, 1.07 and 1.16, respectively simulating slight fuel rich, stoichiometric, and fuel lean conditions. As can be seen, all the perovskite-type OSMs exhibit excellent activities for CO and HC (C.sub.3H.sub.6) oxidation. Complete conversions of CO and HC were observed below 350° C. in all the Pd doped OSMs. The T.sub.50 for C.sub.3H.sub.6 oxidation was as low as 250° C., while for CO oxidation was as low as 240° C. The HC oxidation activities of all the Pd doped CaCo.sub.xZr.sub.1-xO.sub.3-δ-TWCs were comparable to, if not higher than, state-of-the-art TWCs. These promising data clearly confirm the excellent potential for the proposed perovskite TWCs.

(68) Generally, Pd-doped CaCo.sub.xZr.sub.1-xO.sub.3-δ samples showed higher catalytic oxidation activities than Pd-free one at all three conditions, especially at higher SN (fuel lean) conditions. It is obvious that the presence of Pd promotes the surface chemisorption and dissociation/activation of CO and C.sub.3H.sub.8 molecules. The oxidation activity were comparable with CaCo.sub.0.5Zr.sub.0.4Pd.sub.0.1O.sub.3-δ, and CaCo.sub.0.55Zr.sub.0.4Pd.sub.0.05O.sub.3-δ, suggesting mass transfer-limitation with the later sample at the studied conditions. For the same Pd-containing sample, higher conversions were shown at richer condition (SN=0.95), which were most likely because of more accessible active sites generated from “Pd segregation to the surface” at reducing conditions..sup.27,29,36 The Pd-free CaCo.sub.xZr.sub.1-xO.sub.3-δ also showed CO and C.sub.3H.sub.8 conversions, and significantly enhanced conversions when less O.sub.2 was present in the feed (at lean condition). When Pd was absent, surface chemisorption became the rate-limiting step and CO and C.sub.3H.sub.8 from the atmosphere were likely directly oxidized by the surface oxygens newly generated or transferred from the lattice. It is also interesting that at fuel rich (SN=0.95), all samples showed reduced CO conversions and increased H.sub.2 productions at temperature above 400° C., suggesting the occurrence of steam reforming reaction (excess C.sub.3H.sub.8 react with H.sub.2O product from oxidation reaction, to produce H.sub.2 and CO) thermodynamically preferable (endothermic reaction) at higher temperatures. This could be avoided by operating engine mode at stoichiometric conditions.

4. CONCLUSIONS

(69) In this disclosure, CaCo.sub.xZr.sub.1-xO.sub.3-δ, (x=0, 0.3, 0.5, 0.7 and 0.9) perovskites were synthesized for the first time and reported to show improved redox property and oxygen storage capacity (OSC) compared to the state-of-the-art perovskites and ceria-based oxygen storage materials (OSMs). Pd-doped CaCo.sub.0.6-yZr.sub.0.4Pd.sub.yO.sub.3 (y=0.05, 0.1 and 0.2) samples showed promising catalytic activity towards C.sub.3H.sub.6 and CO oxidation under simulated exhaust conditions, suggesting their potential application in three-way catalysis for automotive emissions control.

(70) The studied perovskites retain their main phase of orthorhombic Lakargiite CaZrO.sub.3 structure. Partial substitution of Co by Zr at B sites enhances the perovskite structural crystallinity, but ZrO phase impurity increased with increasing Zr content. For Pd-containing samples, Pd was present as both forms of bulk Pd.sup.2+ and surface Pd.sub.0, and the amount of surface Pd.sup.0 increased with increasing Pd content. When x was around 0.5, perovskites exhibit optimum crystallinity and minimized impurity.

(71) The redox and OSC properties were mainly attributed to B-site Co and Pd. The amount of reducible sites increased with increasing Co contents, while partial substitution with Zr enhanced the reduction of Co species by lowering the reduction temperature. Pd dopant also facilitated the Co reduction and improved the catalyst reducibility. Perovskite-type OSM with composition of CaCo.sub.0.5Zr.sub.0.5O.sub.3 with or without Pd doping gives the optimized reducibility and structural stability. Further kinetics study showed a first order reaction mechanism with an activation energy (Ea) of 0.159 eV for CaCo.sub.0.5Zr.sub.0.5O.sub.3-δ.

(72) Fresh CaCo.sub.0.5Zr.sub.0.4Pd.sub.0.1O.sub.3-δ, CaCo.sub.0.55Zr.sub.0.4Pd.sub.0.05O.sub.3-δ and CaCo.sub.0.5Zr.sub.0.5O.sub.3-δ samples all showed profound conversions of C.sub.3H.sub.6 and CO through catalytic oxidation at fuel lean-rich conditions (SN=1.16, 1.07 and 0.95), with lowest T.sub.50s for C.sub.3H.sub.6 and CO conversions<250° C. Pd-doped perovskites showed higher oxidation activities than Pd-free one at all three conditions, especially at higher SN (lean) conditions. For the same Pd-containing sample, higher conversions were shown at richer condition (SN=0.95), which can be attributed to the reported phenomena of “Pd segregation to the surface”.

7. REFERENCES

(73) (1) Royer, S.; Alamdari, H.; Duprez, D.; Kaliaguine, S. Appl. Catal. B Environ. 2005, 58 (3-4), 273-288. (2) Klimkowicz, A.; Świerczek, K.; Takasaki, A.; Dabrowski, B. Solid State Ion. 2014, 257, 23-28. (3) Hernández, W. Y.; Tsampas, M. N.; Zhao, C.; Boreave, A.; Bosselet, F.; Vernoux, P. Catal. Today 2015, 258, Part 2, 525-534. (4) Mizusaki, J.; Tagawa, H.; Naraya, K.; Sasamoto, T. Solid State Ion. 1991, 49, 111-118. (5) Albrecht, K. J.; Jackson, G. S.; Braun, R. J. Appl. Energy 2016, 165, 285-296. (6) Gálvez, M. E.; Jacot, R.; Scheffe, J.; Cooper, T.; Patzke, G.; Steinfeld, A. Phys. Chem. Chem. Phys. 2015, 17 (9), 6629-6634. (7) Babiniec, S. M.; Coker, E. N.; Miller, J. E.; Ambrosini, A. Sol. Energy 2015, 118, 451-459. (8) McDaniel, A. H.; Ambrosini, A.; Coker, E. N.; Miller, J. E.; Chueh, W. C.; O'Hayre, R.; Tong, J. Energy Procedia 2014, 49, 2009-2018. (9) Demont, A.; Abanades, S. R SCAdv. 2014, 4 (97), 54885-54891. (10) Zheng, Q.; Farrauto, R.; Deeba, M. Catalysts 2015, 5 (4), 1797-1814. (11) Zheng, Q.; Farrauto, R.; Deeba, M.; Valsamakis, I. Catalysts 2015, 5 (4), 1770-1796. (12) Simson, A.; Roark, K.; Farrauto, R. Appl. Catal. B Environ. 2014, 158-159, 106-111. (13) Ran, R.; Wu, X.; Weng, D.; Fan, J. J. Alloys Compd. 2013, 577, 288-294. (14) Keav, S.; Matam, S. K.; Ferri, D.; Weidenkaff, A. Catalysts 2014, 4 (3), 226-255. (15) Levasseur, B.; Kaliaguine, S. Appl. Catal. B Environ. 2009, 88 (3-4), 305-314. (16) Guilhaume, N.; Primet, M. J. Catal. 1997, 165 (2), 197-204. (17) Uenishi, M.; Tanaka, H.; Taniguchi, M.; Tan, I.; Sakamoto, Y.; Matsunaga, S.; Yokota, K.; Kobayashi, T. Appl. Catal. Gen. 2005, 296 (1), 114-119. (18) Tanaka, H.; Taniguchi, M.; Uenishi, M.; Kajita, N.; Tan, I.; Nishihata, Y.; Mizuki, J. 'ichiro; Narita, K.; Kimura, M.; Kaneko, K. Angew. Chem. Int. Ed. 2006, 45 (36), 5998-6002. (19) You, R.; Zhang, Y.; Liu, D.; Meng, M.; Zheng, L.; Zhang, J.; Hu, T. J. Phys. Chem. C 2014, 118 (44), 25403-25420. (20) Nishihata, Y.; Mizuki, J.; Akao, T.; Tanaka, H.; Uenishi, M.; Kimura, M.; Okamoto, T.; Hamada, N. Nature 2002, 418 (6894), 164-167. (21) Glisenti, A.; Pacella, M.; Guiotto, M.; Natile, M. M.; Canu, P. Appl. Catal. B Environ. 2016, 180, 94-105. (22) Li, Z.; Meng, M.; Zha, Y.; Dai, F.; Hu, T.; Xie, Y.; Zhang, J. Appl. Catal. B Environ. 2012, 121-122, 65-74. (23) Shen, S.-T.; Weng, H.-S. Ind. Eng. Chem. Res. 1998, 37 (7), 2654-2661. (24) Tanaka, H.; Mizuno, N.; Misono, M. Appl. Catal. Gen. 2003, 244 (2), 371-382. (25) Tanaka, H.; Misono, M. Curr. Opin. Solid State Mater. Sci. 2001, 5 (5), 381-387. (26) Tanaka, H.; Tan, I.; Uenishi, M.; Kimura, M.; Dohmae, K. Top. Catal. 2001, 16-17 (1-4), 63-70. (27) Li, X.; Chen, C.; Liu, C.; Xian, H.; Guo, L.; Lv, J.; Jiang, Z.; Vernoux, P. ACS Catal. 2013, 3 (6), 1071-1075. (28) Yoon, D. Y.; Kim, Y. J.; Lim, J. H.; Cho, B. K.; Hong, S. B.; Nam, I.-S.; Choung, J. W. J. Catal. 2015, 330, 71-83. (29) Malamis, S. A.; Harrington, R. J.; Katz, M. B.; Koerschner, D. S.; Zhang, S.; Cheng, Y.; Xu, L.; Jen, H.-W.; McCabe, R. W.; Graham, G. W.; Pan, X. Catal. Today 2015, 258, Part 2, 535-542. (30) H. Bork, A.; Kubicek, M.; Struzik, M.; M. Rupp, J. L. J. Mater. Chem. A 2015, 3 (30), 15546-15557. (31) Miura, N.; Ikeda, H.; Tsuchida, A. Ind. Eng. Chem. Res. 2016, 55 (11), 3091-3096. (32) Mota, N.; Barrio, L.; Alvarez-Galvin, C.; Fauth, F.; Navarro, R. M.; Fierro, J. L. G. J. Phys. Chem. C 2015, 119 (29), 16708-16723. (33) Ikeda, H.; Tsuchida, A.; Morita, J.; Miura, N. Ind. Eng. Chem. Res. 2016, 55 (22), 6501-6505. (34) Dey, S.; Naidu, B. S.; Govindaraj, A.; Rao, C. N. R. Phys. Chem. Chem. Phys. 2014, 17 (1), 122-125. (35) Pecchi, G.; Reyes, P.; Zamora, R.; Campos, C.; Cadis, L. E.; Barbero, B. P. Catal. Today 2008, 133-135, 420-427. (36) Sartipi, S.; Khodadadi, A. A.; Mortazavi, Y. Appl. Catal. B Environ. 2008, 83 (3-4), 214-220. (37) Escalona, N.; Fuentealba, S.; Pecchi, G. Appl. Catal. Gen. 2010, 381 (1-2), 253-260. (38) Shen, W.-J.; Okumura, M.; Matsumura, Y.; Haruta, M. Appl. Catal. Gen. 2001, 213 (2), 225-232. (39) Song, H.; Ozkan, U. S. J. Phys. Chem. A 2010, 114 (11), 3796-3801. (40) Mamontov, E.; Egami, T.; Brezny, R.; Koranne, M.; Tyagi, S. J. Phys. Chem. B 2000, 104 (47), 11110-11116. (41) Hu, L.; Zhou, C.; Wu, C.; Zhou, S.; Wang, W. G.; Yin, H. Eur. J. Inorg. Chem. 2015, 2015 (13), 2317-2322. (42) Hancock, J. D.; Sharp, J. H. J. Am. Ceram. Soc. 1972, 55 (2), 74-77. (43) Motohashi, T.; Ueda, T.; Masubuchi, Y.; Kikkawa, S. J. Phys. Chem. C 2013, 117 (24), 12560-12566.

(74) It should be understood that the description above is only representative of illustrative embodiments and examples. For the convenience of the reader, the above description has focused on a limited number of representative examples of all possible embodiments, examples that teach the principles of the disclosure. The description has not attempted to exhaustively enumerate all possible variations or even combinations of those variations described. That alternate embodiments may not have been presented for a specific portion of the disclosure, or that further undescribed alternate embodiments may be available for a portion, is not to be considered a disclaimer of those alternate embodiments. One of ordinary skill will appreciate that many of those undescribed embodiments, involve differences in technology and materials rather than differences in the application of the principles of the disclosure. Accordingly, the disclosure is not intended to be limited to less than the scope set forth in the following claims and equivalents.

INCORPORATION BY REFERENCE

(75) All references, articles, publications, patents, patent publications, and patent applications cited herein are incorporated by reference in their entireties for all purposes. However, mention of any reference, article, publication, patent, patent publication, and patent application cited herein is not, and should not be taken as an acknowledgment or any form of suggestion that they constitute valid prior art or form part of the common general knowledge in any country in the world. It is to be understood that, while the disclosure has been described in conjunction with the detailed description, thereof, the foregoing description is intended to illustrate and not limit the scope. Other aspects, advantages, and modifications are within the scope of the claims set forth below. All publications, patents, and patent applications cited in this specification are herein incorporated by reference as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference.