Combined Capture and Conversion of CO2 to Methanol in a Post Combustion Capture Solvent

Abstract

An efficient and selective catalyst for the condensed phase hydrogenation of captured CO.sub.2 in the presence of an advanced water-lean post combustion capture solvent, EEMPA. Selected heterogenous catalysts for suppress N-methylation of the capture solvent; especially a noble metal on a reducible metal oxide support is highly selective for CN cleavage to produce methanol.

Claims

1. A method of converting CO.sub.2 to methanol comprising: contacting a solution comprising CO.sub.2 in an amine sorbent over a solid catalyst comprising a noble metal on a reducible metal oxide support at a temperature in the range of 181 C. to 225 C.; wherein the CO.sub.2 is post or pre combustion CO.sub.2; and wherein the conversion of CO.sub.2 occurs in a condensed phase and the CO.sub.2 is converted to methanol with at least 40% selectivity; wherein the single pass conversion of CO.sub.2 is at least 75%; and wherein the C.sub.2+ alcohol selectivity, or the ethanol selectivity, is at least 4 mol %.

2. The method of claim 1 further comprising one or any combination of the following: wherein the methanol selectivity is at least 50 mol %; wherein the methanol selectivity is in the range of 40 to about 80 mol %; wherein the single pass conversion of CO.sub.2 is in the range of 75 to about 90%; wherein the selectivity to ethanol is 4 to 10 mol %; wherein the selectivity to butanol is at least 1.7 mol %; wherein the selectivity to butanol is about 2 to about 5 mol %.

3. The method of claim 1 wherein the conversion of CO.sub.2 is in a continuous flow operation.

4. The method of claim 1 occurring in a single pass.

5. The method of claim 1 comprising a single pass CO.sub.2 conversion of 80-90%.

6. The method of claim 1 in which the catalyst support comprises CeO.sub.2 or TiO.sub.2.

7. The method of claim 1 in which the amine sorbent is a water-lean solvent.

8. The method of claim 1 further comprising separation and conversion of CO.sub.2 from landfill gases, waste-water treatment gases, manure off-gas, fermenters, cement plants, steel kilns, and pulp and paper mills.

9. The method of claim 1 in which the amine sorbent is N-(2-EthoxyEthyl)-3-MorpholinoPropan-1-Amine (2-EEMPA).

10. The method of claim 1 in the amine sorbent with 0.5-20wt % CO.sub.2 loading.

11. The method of claim 1 in which ethanol is a co-solvent.

12. The method of claim 1 in which CO and N-formamide are formed as intermediates.

13-18. (canceled)

19. A method of converting CO2 comprising: providing continuous flow reactor system comprising: an absorber; a pump; and a reactor; enriching an amine sorbent with CO.sub.2 by contacting the solvent with a flue gas comprising CO.sub.2 to create a CO.sub.2-enriched solution in the absorber; pressurizing the CO.sub.2-enriched solution to between 30 and 100 bar H.sub.2; heating the CO.sub.2-enriched solution; producing a heated and pressurized CO.sub.2-enriched solution; feeding the heated and pressurized CO.sub.2-enriched solution with pressurized H.sub.2 gas into a reactor comprising a solid catalyst comprising a noble metal on a reducible metal oxide support and reacting the solution over the solid catalyst at a temperature of between 181 and 225 C.; and producing a product solution in which the CO.sub.2 in the solution is converted into methanol, C.sub.2+ alcohols, CH.sub.4, and light hydrocarbons over the solid catalyst.

20. The method of claim 19 comprising a single pass CO.sub.2 conversion of 80-90%.

21. The method of claim 20 in which the conversion of CO.sub.2 occurs in a condensed phase.

22. The method of claim 19 wherein the solid catalyst comprises Pt disposed on a reducible metal oxide support.

23. The method of claim 22 wherein the catalyst support comprises CeO.sub.2 and/or TiO.sub.2.

24. The method of claim 19 wherein the amine sorbent is a water-lean post-combustion solvent.

25-40. (canceled)

41. A composition of matter comprising an amine solvent, CO.sub.2, and a heterogenous catalyst, and methanol derived from the carbon dioxide, wherein the methanol derived from the CO.sub.2 makes up at least 1% of mass percent of the CO.sub.2 and wherein the molar ratio of the methanol produced from CO.sub.2 to ethyl formate in the composition is greater than 2.

42. The composition of claim 41 in which the catalyst suppresses N-methylation of capture solvent.

43-45. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG. 1: Proposed gas phase (A) and condensed-phase (B) methanol synthesis from CO.sub.2 and H.sub.2.

[0032] FIG. 2: Reaction mechanism of post-combustion solvent system.

[0033] FIG. 3: Process flow diagram of the IC.sup.3M CO.sub.2 capture and conversion to methanol process.

[0034] FIG. 4: Hydrogenation of captured CO.sub.2 in the presence of Cu- and Ag-supported heterogeneous catalysts using a batch reactor system.

[0035] FIG. 5: Reaction mechanism with ethanol co-feed.

[0036] FIG. 6: In situ .sup.13C MAS-NMR during the hydrogenation of .sup.13CO.sub.2 in the presence of 2-EEMPA and the Cu/ZnO/Al.sub.2O.sub.3 catalyst at 170 C. under 60 bar H.sub.2 (initial pressure) in ethanol co-solvent, 2-EEMPA:EtOH=1:10 (molar ratio).

[0037] FIG. 7: NH.sub.3-TPD (FIG. 7A) and CO.sub.2-TPD (FIG. 7B). Conditions: Ammonia (10 mol % NH.sub.3 in He) and CO.sub.2 (10 mol % CO.sub.2 in He) were adsorbed on 100 mg of sample. We loaded 100 mg of sample and purged under flowing He (25 sccm) for 10 min. Samples were pretreated in situ at 200 C. with 10% O.sub.2/He for 2 h, followed by reduction at 200 C. with 10% H.sub.2/N.sub.2 for 20 min, He purge at 200 C. for 10 min, then cooled to 40 C. for NH3 or CO2 chemisorption. After the adsorption, samples were purged under flowing He (25 sccm) for 10 min, then the samples were heated up to 500 C. at a rate of 10 C./min. Resulting NH.sub.3 and CO.sub.2 uptakes are presented in Table 4. (TPD=temperature programmed desorption)

[0038] FIG. 8: .sup.1H NMR of the crude reaction mixture (from Table 5, entry 8) in CD.sub.3CN.

[0039] FIG. 9: Proposed reaction mechanism for the hydrogenation of captured CO.sub.2 in the presence of Pt/TiO.sub.2 catalyst. Surface hydroxyl groups are not shown for simplicity.

[0040] FIG. 10: In situ .sup.13C MAS-NMR during the hydrogenation of .sup.13CO.sub.2 in the presence of 2-EEMPA and a 5wt % Pt/TiO.sub.2 catalyst at 170 C. under 60 bar H.sub.2 (initial pressure) in an ethanol co-solvent, 2-EEMPA:EtOH=1:10 (molar ratio).

[0041] FIG. 11: XRD spectra of fresh and spent Pt/TiO.sub.2 catalysts used in experiments in Table 8 (entries 6-8). (XRD=X-ray powder diffraction)

[0042] FIG. 12: CO-TPD for the Pt/TiO.sub.2 catalyst (from Table 7, entry 1). TPD conditions: after CO chemisorption saturation at 40 C., samples were purged under flowing He (25 sccm) for 10 min, then the samples were heated up to 250 C. at a rate of 10 C./min in flowing He (25 sccm).

[0043] FIG. 13: Continuous flow reactor set up. Reaction setup consists of a downstream fixed bed reactor. Catalyst (1-5 g) was loaded inside a (in) stainless steel tube, pressure was maintained using a Tescom back pressure regulator. Gases and liquid were fed using gas mass flow controllers (Brooks) and a syringe pump (ISCO Teledyne) (0-100 sccm and 0-1 mL/min, respectively). Liquid sample was collected periodically from a 50 mL collection pot downstream the reactor (50 mL, 0-10 C.). Gas sample was analyzed with a microGC instrument (Fusion

[0044] Inficon).

[0045] FIG. 14: Diffuse reflectance infrared Fourier Transform Spectroscopy (DRIFTS) spectra of fresh (blue spectrum, after post-synthesis calcination) and spent (red spectrum, collected from reactor after reaction) Pt/TiO.sub.2 catalysts used in experiments presented in Table 7 (entries 6-8).

[0046] FIG. 15: TPO-MS profiles of the fresh and spent Pt/TiO.sub.2 catalysts used in experiment C. in Table 7 (entries 6-8). Using 50 sccm of a mixture of 10 % O2/He (50 cc min.sup.1), 50 mg of the samples were ramped to 600 C. (10 C. min.sup.1). (TPO-MS=temperature-programmed oxidation with mass spectrometry)

DETAILED DESCRIPTION OF THE INVENTION

[0047] The amine may comprise a polyamine, a tertiary amine, an alkanolamine, an aminopyridine, a diamine compound according to Formula I, or any combination thereof, the compound according to Formula I having a structure R.sup.1(R.sup.2)N-L.sup.1-NHR.sup.3 where each of R.sup.1 and R.sup.2 independently is aliphatic or cycloaliphatic or R.sup.1 and R.sup.2 together with the nitrogen to which they are attached form a heterocyclic ring, L.sup.1 is aliphatic or cycloaliphatic or L.sup.1 and R.sup.1 together with the nitrogen to which they are attached form a heterocyclic ring, and R.sup.3 is aliphatic, cycloaliphatic, cycloalkylalkyl or alkoxyalkyl. In certain embodiments, the amine is not an amidine, since amidines may decompose under the reaction conditions.

R.sup.1(R.sup.2)N-L.sup.1-NHR.sup.3 (Formula I)

[0048] With respect to Formula I, each of R.sup.1 and R.sup.2 independently is aliphatic, preferably alkyl, such as C.sub.1-6alkyl, C.sub.1-4alkyl, C.sub.1-3alkyl, or C.sub.1-2alkyl; cycloaliphatic, preferably cycloalkyl, such as C.sub.3-7cycloalkyl or C.sub.3-4cycloalkyl, and may be cyclopropyl; or R.sup.1 and R.sup.2 together with the nitrogen to which they are attached, form a heterocyclic ring, such as an non-aromatic heterocyclic ring, preferably a 5- or 6-membered heterocyclic ring and optionally comprising one or more additional heteroatoms, such as 1 or 2 heteroatoms selected from oxygen, nitrogen or sulfur, and/or optionally substituted with alkyl, such as C.sub.1-4alkyl. Alternatively, R.sup.1 may form a heterocyclic moiety, with L.sup.1, such as a non-aromatic heterocyclic moiety, preferably a 5- or 6-membered heterocyclic moiety. In such embodiments, R.sup.2 is aliphatic, preferably alkyl, such as C.sub.1-6alkyl, C.sub.1-4alkyl, C.sub.1-3alkyl, or C.sub.1-2alkyl, or cycloalkyl, such as C.sub.3-7cycloalkyl.

[0049] Each of R.sup.1 and R.sup.2 independently is linear alkyl or branched alkyl, such as C.sub.1-6linear alkyl, or C.sub.3-6branched alkyl. Exemplary linear alkyl moieties include, but are not limited to methyl, ethyl, n-propyl or n-butyl, and exemplary branched alkyl moieties include, but are not limited to, isopropyl, tert-butyl, iso-butyl, or sec-butyl. And R.sup.1 and R.sup.2 may be the same or different. In other embodiments, R.sup.1 and R.sup.2 together with the nitrogen to which they are attached form a non-aromatic heterocyclic moiety, such as morpholine, thiomorpholine, piperidine, pyrrolidine, or piperazine, optionally substituted with C.sub.1-4alkyl, typically, methyl, ethyl, isopropyl, or tert-butyl.

[0050] L.sup.1 is aliphatic, preferably alkyl, such as C.sub.2-4alkyl or C.sub.2-3alkyl; cycloaliphatic, preferably cycloalkyl, such as C.sub.5-7cycloalkyl; or L.sup.1 and R.sup.1 together with the nitrogen to which they are attached form a non-aromatic heterocyclic ring, such as a 5-, 6-, or 7-membered heterocyclic, optionally comprising one or more additional heteroatoms, such as 1 or 2 heteroatoms selected from oxygen, nitrogen or sulfur. In some embodiments, L.sup.1 is CH.sub.2CH.sub.2 or CH.sub.2CH.sub.2CH.sub.2, but in other embodiments, L.sup.1 and R.sup.1 together with the nitrogen to which they are attached, form a 5- or 6-membered non-aromatic heterocyclic ring, such as a piperidine or pyrrolidine ring. In some such embodiments, R.sup.2 is C.sub.1-6alkyl, such as C.sub.1-4alkyl, C.sub.1-3alkyl, or C.sub.1-2alkyl, preferably methyl or ethyl.

[0051] R.sup.3 is aliphatic, cycloaliphatic, cycloalkylalkyl or alkoxyalkyl. In some embodiments, R.sup.3 is alkyl, such as C.sub.1-6alkyl, C.sub.1-4alkyl, C.sub.1-3alkyl, or C.sub.1-2alkyl; cycloalkyl, such as C.sub.3-7cycloalkyl or C.sub.3-4cycloalkyl; cycloalkylalkyl, such as CH.sub.2cycloalkyl; or alkoxyalkyl, such as C.sub.1-6alkyl, C.sub.1-4alkyl, C.sub.1-3alkyl, or C.sub.1-2alkyl substituted C.sub.1-4alkoxy, C.sub.1-2alkoxy, or C.sub.3-6cycloalkyl. R.sup.3 may be linear or branched alkyl, and may be a linear C.sup.1-6alkyl, C.sub.1-4alkyl, C.sub.1-3alkyl, or C.sub.1-2alkyl or a branched C.sub.3-6alkyl, C.sub.3-4alkyl, or C.sub.3alkyl. Exemplary linear and branched alkyl moieties include, but are not limited to, methyl, ethyl, n-propyl, or n-butyl, and isopropyl, isopropyl, tert-butyl, iso-butyl, or sec-butyl. In some embodiments, R.sup.3 is unsubstituted, but in other embodiments, R.sup.3 is substituted, and may be substituted with alkoxy, such as C.sub.1-4alkoxy, or C.sub.1-2alkoxy. Exemplary alkoxy substituents include, but are not limited to, methoxy, ethoxy, propoxy, isopropoxy or cycloalkoxy, such as cyclopropoxy.

[0052] Nonlimiting Exemplary compounds within the scope of Formula I include:

##STR00001## ##STR00002##

[0053] The amine sorbent can be combined with a solvent, i.e. a co-solvent or co-feed, to form a liquid sorbent solution. The co-solvent or co-feed can be any alcohol-containing species, including but not limited to aliphatic, aromatic or other polymeric or polyols, or any combination thereof. For example, a preferred co-feed is ethanol. It was observed that an ethanol co-feed facilitates reaction through formate ester intermediate, which was more selective to methanol than N-formamide intermediate. (FIG. 5)

[0054] The catalyst used in the conversion of CO.sub.2 to products comprises a noble metal disposed on a reducible oxide support. Preferably, the catalyst comprises from 1 to 20 wt % noble metal, more preferably 1 to 10 wt %. The noble metal can be any of the noble metals or any combination of the noble metals.

[0055] The catalyst may be described by any of the properties reported herein, or within 30% or 20% or 10% of any of the measurements described herein.

Properties of Reaction

[0056] The reactions can be characterized by one or any combination of the following: an amine sorbent preferably with at least 2 wt %, or at least 5 wt %, or in the range of 3 to 15 wt % CO.sub.2 loading; a reaction temperature of at least 140 C., or preferably at least 160 C., or in the range of 120 to 200 C.; a reaction pressure of at least 30 bar H.sub.2, or preferably at least 50 bar H.sub.2, or in the range of 30-100 bar H.sub.2.

[0057] The reactions can be further characterized by one or any combination of the following: Selectivity to methanol from CO.sub.2 is preferably at least 50%, or at least 60%, or in the range of 50 to about 95%, or 60 to about 95%. WHSV (weight hourly space velocity in units of g CO.sub.2/g cat/h) of at least 0.005, or at least 0.010, or in the range of 0.010 to 0.50, or in the range of 0.010 to 0.20, or in the range of 0.010 to 0.10.

[0058] The catalyst and process were demonstrated to be selective towards methanol with 93% selectivity at 140 C. At 190 C., the CO.sub.2 conversion increased from 12% to 86% when space velocity was decreased by a factor of 10. Conversion decreased from 86% to 65% over a span of approximately 40 hours.

[0059] In FIG. 3, 90% CO.sub.2 in the flue gas from a NGCC power plant is captured in the absorber by countercurrent contact with an amine sorbent solution, producing a CO.sub.2-rich solvent. The condensed-phase CO.sub.2-rich solvent is pumped to the desired pressure to avoid the use of a capital and energy-intensive CO.sub.2 compressor. The pressurized CO.sub.2-rich solvent is then heated and fed to the main reactor packed with Pt/TiO.sub.2 catalyst at 190 C., 60 bar along with H.sub.2. In this analysis, H.sub.2 is produced off-site from either fossil or renewable pathway, which is outside the system boundary. It is assumed that H.sub.2 is delivered at the conversion plant at pressure as required for H.sub.2 transportation..sup.[31] The reactor product contains CO.sub.2-lean solvent, unconverted H.sub.2. methanol, C.sub.2+ alcohols, CH.sub.4, and light hydrocarbons. The product is first sent to a high-pressure flash drum, where the gas phase goes to the pressure swing adsorption (PSA) unit to separate unconverted H.sub.2 from CH.sub.4 and light hydrocarbons. The H.sub.2 is recycled back to the reactor, while CH.sub.4 and light hydrocarbons are used as fuel gas to supply heat and energy for other unit operations. The liquid phase from the high-pressure flash drum is sent to the solvent recovery column to separate alcohols from the CO.sub.2-lean solvent. The lean solvent from the bottom is recycled back to the absorber for CO.sub.2 capture. Wet alcohols from the top contain mainly methanol, ethanol, and water. Because of the existence of azeotrope between these components, extractive distillation is used for alcohols and water separation, where ethylene glycol is used as an entrainer.

Materials and Analytical Techniques

[0060] Materials: 64 wt % Cu/Zn/Al.sub.2O.sub.3 was purchased from Alfa Acsar. 2-EEMPA was synthesized by following the procedure reported in the literature..sup.[16a] Metal (Pt, Pd, Ni, Cu) supported on metal oxides (TiO.sub.2, Al.sub.2O.sub.3, CeO.sub.2, SiO.sub.2, MgO) were prepared by incipient wetness impregnation of nitrate metal precursors followed by drying (8 h at 100 C.) and calcination at 400 C. (4 h under static air). Metal oxide supports: TiO.sub.2=Degussa P25 from Sigma Aldrich, Al.sub.2O.sub.3=-Al.sub.2O.sub.3 from Engelhard, CeO.sub.2=nanopowder (<25 nm) from Sigma Aldrich, SiO.sub.2=Davisil 646 Silica gel from Sigma Aldrich, MgO=Nanoactive (R) MgO from Nanoscale

[0061] Corporation. All other materials were purchased from commercial suppliers and used without further purification unless otherwise mentioned. All deuterated solvents were purchased from Cambridge Isotope Laboratories, Inc. 1,3,5-Trimethoxybenzene (TMB) was added as an internal standard for NMR spectroscopy.

[0062] The Cu/Zn/Al catalyst, which was derived from a hydrotalcite precursor with a Cu.sup.2+/Zn.sup.2+ atomic ratio of 2 (56% wt Cu), was prepared by a co-precipitation method at room temperature using nitrate precursors and a basic precipitation solution (2 m NaOH, 0.5 m Na.sub.2CO.sub.3). The precipitation product was aged (80 C.), washed, and dried overnight. The resulting precipitate hydroxide (layered hydroxide) was then calcined at 450 C. for 4 h to generate a combination of oxides.

[0063] Standard Procedure for Batch Experiments: A Parr reactor.sup.[34] (100 mL) equipped with a thermocouple, pressure transducer, and reactor controller, was charged with a catalyst and CO.sub.2 loaded capture solvent and sealed in a N.sub.2-atmosphere glovebox. The reactor was then pressurized with H.sub.2 (60 bar) and heated to 170 C. The reactor was cooled to room temperature, and the gas in the reactor headspace was analyzed using a 2-channel Fusion MicroGC (Inficon). The remaining excess gas was slowly released after cooling the reactor to 78 C. TMB was dissolved in acetonitrile and added as an internal standard to the reaction mixture, and a small aliquot of the sample was analyzed by .sup.1H and .sup.13C NMR experiments in CD.sub.3CN.

[0064] Procedure for In Situ High-Pressure and High-Temperature MAS-NMR: The MAS-NMR experiments were performed on an Agilent-Varian VNMRS NMR spectrometer equipped with a 7.05 T magnet, operating at 75.43 MHZ for the .sup.13C channel and 299.969 MHz for the .sup.1H channel, and using a 5 mm Chemmagnetics design HXY probe. The rotors were Varian/Agilent style cavern rotors (Revolution NMR LLC), modified for high-pressure samples as described previously..sup.[35] 2-EEMPA (0.16 mmol), Cu/ZnO/Al.sub.2O.sub.3 or Pt/TiO.sub.2 (8 mg), and ethanol (1.6 mmol) were transferred to a MAS-NMR rotor in a N.sub.2-atmosphere glovebox. The rotor was charged with a .sup.13CO.sub.2 (0.28 mmol) and H.sub.2 (0.8 mmol) at room temperature and heated to 170 C. When the set temperature was reached, the rotor was kept at this temperature while an array of .sup.13C NMR spectra was collected. A 45 pulse was used. A recycle delay of 30 s and a spinning speed of 5 kHz were applied. The spectra were acquired with 64 scans and an acquisition time of 300 ms.

[0065] Standard Procedure for Continuous-Flow Experiments: Fixed-bed experiments were performed in a stainless-steel tubular reactor (3/8 nominal OD, 0.305 ID), the reactor wall was heated with a stainless-steel block (3 in) wrapped with a fiberglass heating tape (Omegalux) (FIG. 13). Liquid was fed to the reactor using a high-pressure Isco pump (Teledyne), and gases (H.sub.2, N.sub.2) were fed using mass flow controllers (Brooks). In a typical experiment, 1 g of catalyst (60-100 mesh) was loaded between quartz wool in the heated part of the reactor. Reaction conditions: pressure (60 bar) was controlled using a Tescom back pressure regulator, and temperature (120-190 C.) was controlled using a digi-sense R/S controller. After reaction, liquid products were condensed and collected in a stainless-steel 50 mL cylinder maintained at 0 C. using a recirculatory thermostat (VWR). Gas products were analyzed using a 4-channel Fusion MicroGC (Inficon), and liquid products were analyzed using liquid chromatography.

[0066] Catalysts Characterization: Fresh and spent samples of Pt/TiO.sub.2 catalyst were studied using DRIFTS, TPO-MS, XRD, ICP, and CNHSO elemental analysis.

[0067] The DRIFTS accessory was a Harrick Praying Mantis with a reaction chamber and zinc selenide windows adapted to a Bruker IFS 66/S spectrometer. The spectra of the untreated samples were recorded with the sample at room temperature (21 C.) and at atmospheric pressure using a background with potassium bromide powder and dry nitrogen purge. The instrument resolution was 4 cm.sup.1 with an 8 mm aperture, and 1024 scans were co-added for the spectrum. A silicon carbide source was used with a KBr beam splitter and a liquid-nitrogen-cooled MCT detector. The scanner velocity was 60 kHz. The phase resolution was 32 cm.sup.1 with a Mertz phase correction. A Blackman-Harris-3-term apodization function was used with 2 zerofill. The nonlinearity correction was turned on.

[0068] TPO-MS was performed using a Micromeritics Autochem II 2920 chemisorption analyzer coupled with a Cirrus 2 Mass Spectrometer. 50 mg of sample was loaded under 50 sccm 10% O.sub.2/He for 40 min, and without any preliminary thermal treatment, the sample was ramped up to 600 C. at a rate of 10 C. min.sup.1 and held at this temperature for 20 min. Effluent gases were monitored using mass spectrometry.

[0069] TPD and CO Chemisorption were performed using a Micromeritics Autochem II 2920 chemisorption analyzer. 100 mg of sample was loaded and was purged under flowing He (25 sccm) for 10 min. Samples were pretreated in situ at 200 C. with 10% O.sub.2/He for 2 h, followed by reduction at 200 C. with 10% H.sub.2/N.sub.2 for 20 min, He purge at 200 C. for 10 min, then cooled to 40 C. for NH.sub.3 or CO.sub.2 or CO chemisorption. After the adsorption, samples were purged under flowing He (25 sccm) for 10 min, then the samples were heated up to 500 or 250 C. at a rate of 10 C. min.sup.1.

[0070] XRD patterns were recorded using a Philips X'pert MPD (Model PW3040/00) diffractometer with a copper anode (Ka1=0.15405 nm) and a scanning rate of 0.0013 per second between 2 h=10 and 90. Jade 5 (Materials Data Inc., Livermore, CA) and the Powder Diffraction File database (International Center for Diffraction Data, Newtown Square, PA) were used to analyze the diffraction patterns.

[0071] The carbon, hydrogen, nitrogen, and sulfur composition of the Pt/TiO.sub.2 catalyst before and after reaction was determined using a Thermo Fisher Flash 2000 CHNS/O organic elemental analyzer (Thermo Fisher Scientific, Inc., Waltham, MA). About 10 mg of sample was used for cach analysis.

[0072] ICP (inductively coupled plasma) was used to quantify the amount of Pt present on the Pt/TiO.sub.2 catalyst before and after reaction. ICP used a Perkin-Elmer 3000DV with an AS90 Autosampler, which has an instrument detection limit of 1 ppb. About 10 mg of solid sample was prepared via microwave digestion in concentrated acid and then diluted to volume.

Examples and Discussion

[0073] The hydrogenation of captured CO.sub.2 was studied using EEMPA as a water-lean post combustion capture solvent. First, the CO.sub.2 captured in EEMPA solvent (10 wt % CO.sub.2 loading) was subjected to hydrogenation in the presence of an industrial gas phase methanol catalyst, Cu/ZnO/Al.sub.2O.sub.3 (entry 1, table 1). The undesired N-methylation of EEMPA was observed as a major product by .sup.1H NMR. To confirm N-methylation, operando NMR was performed with .sup.13C-enriched CO.sub.2 (shown in FIG. 6). At 25 C., under .sup.13CO.sub.2 and H.sub.2 atmosphere, mostly the EEMPACOO-(carbamate) species was observed at 159.2 ppm in addition to .sup.13CO.sub.2 at 125.2 ppm. Upon heating this to 170 C., the following new species were observed: .sup.13CO, EEMPA+H.sup.13CO.sub.2 (formate), H.sup.13CO.sub.2C.sub.2H.sub.5 (ester), EEMPA-.sup.13CHO (formamide) and EEMPA-.sup.13CH.sub.3 (N-methylated EEMPA). The major species was the EEMPA-.sup.13CH.sub.3 (the .sup.13CH.sub.3 signal observed at 41.7 ppm), which was formed as a result of .sup.13CO.sub.2 acting as a N-methylating agent. Similar N-methylation of amines was reported in the literature with Cu/Al.sub.2O.sub.3 catalyst..sup.[2] Literature reports have also shown that the rate of formation of N-methylated amine increased (and methanol decreased) at higher temperature, but the mechanism for the N-methylation is still not known..sup.[3] It is also believed that the in situ formed methanol can act as a N-methylating agent. The fact that operando NMR studies only showed traces of methanol, but excess of EEMPA-.sup.13CHO species, it is likely the N-methylation occurs through the formamide intermediate. The formamide can undergo CO cleavage to form N-methylated amine or CN cleavage to form methanol (FIG. 1). The CN cleavage is preferred as CO cleavage results in deactivation of the capture solvent via N-methylation.

[0074] Under the experimental conditions shown in Table 1, entry 1, the CN cleavage selectivity was 25% in the case of Cu/ZnO/Al.sub.2O.sub.3. A CO formation was also observed via the reverse water gas shift reaction (RWGS) as a side product. The use of other amphoteric oxide supports such as hydrotalcite and ZrO.sub.2 resulted in suppression of methanol product and only N-formamide and EEMPA-N-Me products were observed in addition to CO (Table 1, entries 2 and 4). A decreased CO.sub.2 loading (5 wt %) improved the overall conversion and reduced RWGS reaction although the CN cleavage selectivity remained mostly unchanged (Table 1, entry 1 vs 3). The acidic supports such as CeO.sub.2 and TiO.sub.2 completely suppressed both the methanol and EEMPA-Me formation, however the EEMPA-CHO was observed as a major product in both cases, which indicates that these supports in combination with Cu are not effective for the hydrogenation of the formamide intermediate under these reaction conditions (Table 1, entries 5 and 6). Overall, the surface acidity/basicity of the oxide supports considerably influenced the performance and selectivity of the catalyst (Table 1, entries 1-6).

[0075] Milstein et al. have shown that Ag/Al.sub.2O.sub.3 catalyst was effective for the selective CN cleavage in the case of hydrogenation of benzamides and aliphatic amides under basic conditions..sup.[4] Because formamide is an important intermediate observed under our reaction conditions, 30 wt % Ag/Al.sub.2O.sub.3 was screened for the hydrogenation of captured CO.sub.2 to improve the CN cleavage selectivity for the hydrogenation of in-situ formed formamide intermediate, EEMPA-CHO (Table 1, entry 7). Unfortunately, Ag/Al.sub.2O.sub.3 was very slow for the hydrogenation of EEMPA-CHO. In addition, there was no selectivity for CN cleavage resulting in N-methylation of EEMPA.

TABLE-US-00001 TABLE 1 Hydrogenation of captured CO.sub.2 in the presence of Cu and Ag catalysts using batch reactor system. CN CO2 Product selectivity (%) Methanol cleavage Exp. conv. EEMPA- EEMPA- Yield selectivity Entry No. Catalyst (%) CO CH.sub.4 CHO Me Methanol (%) (%) 1.sup.a 218 64 wt % 40.2 21.4 0.0 0.0 59.0 19.6 7.9 24.9 Cu/ZaO/Al.sub.2O.sub.3 2.sup.a 251 Cu/ZaO/hydrotalcite 34.2 16.3 4.7 15.7 63.3 0.0 0.0 0.0 3.sup.b 283 64 wt % 62.3 14.2 0.0 0.0 65.8 20.0 12.5 23.3 Cu/ZnO/Al.sub.2O.sub.3 4.sup.b 263 Cu/Za/ZrO.sub.2 60.5 10.7 0.0 31.2 58.1 0.0 0.0 0.0 5.sup.b 270 5 wt % Cu/CeO.sub.2 3.4 0.0 0.0 100.0 0.0 0.0 0.0 6.sup.b 281 35 wt % Cu/TiO.sub.2 15.7 5.6 0.0 76.6 17.8 0.0 0.0 0.0 7.sup.b 261 30 wt % Ag/Al.sub.2O.sub.3 30.6 0.0 1.0 72.8 26.3 0.0 0.0 0.0 Conditions: catalyst = 200 mg, 170 C., EEMPA-5 g (CO.sub.2 loaded EEMPA used), initial P(H.sub.2) = 60 bar, time = 12 h, .sup.aEEMPA-(10 wt %) CO.sub.2, .sup.bEEMPA-(6 wt %) CO.sub.2, Cu/ZnO/Al.sub.2O.sub.3 = Cu (64 wt %)/ZnO(24 wt %)/Al.sub.2O.sub.3(5 wt %), [0076] Traditional gas-phase CO.sub.2 hydrogenation catalysts deactivated the solvent via N-methylation of the 2 amine moiety. [0077] Higher conversion demonstrated at lower CO.sub.2 loading. [0078] The methanol selectivity compared to EEMPA N-Me was <25% in all these cases.

TABLE-US-00002 TABLE 2 Ethanol co-feed facilitates methanol production. N- CH.sub.3OH Capture Exp. CO.sub.2/H.sub.2 Time Formamide methylamine CH.sub.3OH Selectivity Entry Solvent No. (bar) (h) (mmol) (mmol) (mmol) (%) 1 EEMPA 62711- 15/45 12 0.8 2 0.65 24.5 153 2 EEMPA 62711- 15/45 48 0.45 5.1 1.23 19.4 148 3 EEMPA 62711- 5/55 48 0.04 5.85 1.19 16.9 147 4.sup.a EEMPA + 62711- 5/55 48 traces 1 2.4 70.6 ethanol 150 Catalyst: Cu/ZnO/Al.sub.2O.sub.3 = 200 mg, 100 mL reactor, EEMPA = 23 mmol, P = 60 bar (CO.sub.2:3H.sub.2), T = 170 C., t = 12 h, .sup.aethanol = 200 mmol, only the liquid phase CO.sub.2 derived products shown. [0079] Ethanol co-feed facilitates reaction through formate ester intermediate, which was more selective to methanol than N-formamide intermediate. [0080] With leading PNNL post-combustion system EEMPA, process conditions tailored to form methanol with 71% selectivity. [0081] The formation of methanol in the presence of a post combustion solvent has, we believe, been demonstrated for the first time in the presence of a heterogenous catalyst.

[0082] Several different co-feeds and process conditions were evaluated with goal to improve methanol selectivity through N-formamide intermediate. [0083] N-formamide is harder to reduce versus formate ester [0084] Selectivity and conversion is higher if we form the ester species [0085] Using ethanol would complicate the processing and add costs 5 wt % Pd/Zn/Al.sub.2O.sub.3 was screened for the hydrogenation of captured CO.sub.2 (Table 3, entry 1). The selectivity and performance of the 5 wt % Pd/ZnO/Al.sub.2O.sub.3 was comparable to that of Cu/ZnO/Al.sub.2O.sub.3. Upon testing the roles of Al2O3 and ZnO with 5 wt % Pd separately, it was revealed that the combination of both Al.sub.2O.sub.3 and ZnO were required for higher CO.sub.2 conversion (Table 3, entries 2 and 3). In particular, the CN cleavage selectivity was further reduced with 5 wt % Pd/Al.sub.2O.sub.3 catalyst. The Pd on Ga.sub.2O.sub.3 support predominately formed methane and some amount of CO. No N-methylation was observed in this case. A lower CO.sub.2 loading (Table 3, entry 5) showed no improvement in the CO.sub.2 conversion unlike the Cu/ZnO/Al.sub.2O.sub.3 catalyst (in Table 1, entries 1 and 3) suggesting possibly different mechanistic pathways involved irrespective of similar product distributions with Pd/Zn/Al.sub.2O.sub.3 and Cu/ZnO/Al.sub.2O.sub.3 catalysts.

[0086] The Pd on an inert support, carbon, formed EEMPA-Me with good selectivity along with small amounts of CO and methane as side products (Table 1, entry 8). A basic support such as MgO significantly improved the CN cleavage selectivity to 55% (Table 1, entry 9) although the methanol yield was lower than the entry 1, Table 3 with 5wt % Pd/ZnO/Al.sub.2O.sub.3. Similar to the basic support, the Pd on an acidic support (CeO.sub.2) also remarkably improved the CN cleavage selectivity to 70%, resulting in significant suppression of the N-methylation.

TABLE-US-00003 TABLE 3 Hydrogenation of captured CO.sub.2 in the presence of Pd catalysts using batch reactor system. CN CO2 Product selectivity (%) Methanol cleavage Exp. conv. EEMPA- EEMPA Yield selectivity Entry No. Catalyst (%) CO CH.sub.4 NCHO NMe Methanol (%) (%) 1.sup.a 172 5 wt % 54.3 14.3 0.2 22.9 52.0 10.4 5.7 16.7 Pd/ZnO/Al.sub.2O.sub.3 2.sup.a 255 5 wt % Pd/Al.sub.2O.sub.3 30.5 6.0 1.9 50.6 37.7 3.8 1.2 9.1 3.sup.a 174 5 wt % Pd/ZnO 20.7 38.7 0.0 5.3 42.8 13.2 2.7 23.5 4.sup.a 249 5 wt % Pd/Ga.sub.2O.sub.3 9.3 14.0 86.0 0.0 0.0 0.0 0.0 5.sup.b 254 5 wt % Pd/Zn/Al.sub.2O.sub.3 55.3 13.3 2.6 13.7 60.0 10.4 5.8 14.8 6.sup.b 272 5 wt % 3.3 40.2 20.1 39.7 0.0 0.0 0.0 Pd/hydrotalcite 7.sup.b 260 5 wt % Pd/ZnO/ 39.8 14.4 1.1 9.9 64.5 10.1 4.0 13.5 Al.sub.2O.sub.3 (reduced at 400 C.) 8.sup.b 269 5 wt % Pd/C 18.5 4.4 2.4 0.0 93.2 0.0 0.0 0.0 9.sup.b 271 5 wt % Pd/MgO 13.3 8.3 5.5 57.2 13.2 15.8 2.1 54.5 10.sup.b 266 5 wt % Pd/CeO.sub.2 16.5 11.6 4.0 45.9 10.6 28.0 4.6 72.6 11.sup.b,c 267 5 wt % Pd/CeO.sub.2 25.4 5.8 1.3 59.9 10.3 22.7 5.8 68.8 .sup.aEEMPA-CO.sub.2, .sup.bEEMPA-1/2CO.sub.2, .sup.cethanol, 5 wt % Pd/ZnO/Al.sub.2O.sub.3 = 200 mg, Pd/Zn ratio = 0.25

[0087] Pt/CeO.sub.2 was screened under similar reaction conditions (Table 5, entry 1). Similar to Pd/CeO.sub.2, Pt/CeO.sub.2 formed methanol with high CN bond cleavage selectivity. In addition, a considerable amount of CO was also formed in the gas phase by the rWGS reaction. The CO formation via decarbonylation of methanol has been reported in the literature..sup.[21] The TiO.sub.2 support behaved similar to CeO.sub.2, albeit with more methane formation and less CO production (Table 5, entry 1 vs. 2). While no methanol was formed in the case of Pt on a SiO.sub.2 support, more CO was formed relative to Pt on a TiO.sub.2 support (Table 1, entry 2 vs. 3). In order to understand the role of the support on the reaction mechanism, we performed CO.sub.2-TPD (TPD=temperature programmed desorption) and NH.sub.3-TPD to evaluate the acidic and basic nature of the Pt/TiO.sub.2, Pt/SiO.sub.2 and Pt/CeO.sub.2 catalysts (FIGS. 7A and 7B, Table 4). The TPD analyses showed that Pt/TiO.sub.2 has both acidic and basic sites, while the Pt/CeO.sub.2 catalyst contains mostly basic sites and the Pt/SiO.sub.2 does not have acidic or basic sites. This suggests that the basicity offered by the TiO.sub.2 and CeO.sub.2 supports suppresses N-methylation (see FIG. 1). Based on the experimental and TPD results, a plausible reaction mechanism for the methanol, CO and CH.sub.4 formation from the captured CO.sub.2 has been shown in FIG. 9. First, the captured CO.sub.2 (i.e, carbamate) coordinates to the catalyst surface, followed by hydrogenation with hydrogen activated by Pt to form a formate species, B. The in situ formed formate species, B, formylates the amine and forms an N-formamide intermediate, E. The nucleophilic attack of the lattice oxygen of the support on the carbonyl carbon of the N-formamide intermediate, E, and subsequent hydrogenation and deamination results in the formaldehyde intermediate, H, which then gets hydrogenated again to form methanol. We believe the participation of the lattice oxygen in the nucleophilic attack of the carbon of the N-formamide intermediate is the key to the CN cleavage selectivity. Recent reports in the literature for alcoholysis of amides have indicated that both basic and acidic sites offered by CeO.sub.2 surfaces are required for selective CN cleavage. However, the mechanistic understanding on the synergistic effect between Pt and the acid-base pairs offered by the supports requires further investigation.

TABLE-US-00004 TABLE 4 Acidity and basicity of 5 wt % Pt catalysts using NH.sub.3 and CO.sub.2 TPD. Acidity Basicity NH.sub.3-TPD CO.sub.2-TPD Entry Catalysts (mol/g) (mol/g) 1 5 wt % Pt/TiO.sub.2 24.4 5.6 2 5 wt % Pt/CeO.sub.2 2.7 6.1 3 5 wt % Pt/SiO.sub.2 n.d n.d 100 mg of sample loaded and purged under flowing He (25 sccm) for 10 min. Samples were pretreated in situ at 200 C. with 10% O.sub.2/He for 2 h, followed by reduction at 200 C. with 10% H.sub.2/N.sub.2 for 20 min, He purge at 200 C. for 10 min, then cooled to 40 C. for NH.sub.3 or CO.sub.2 chemisorption. After the adsorption, samples were purged under flowing He (25 sccm) for 10 min, then the samples were heated up to 500 C. at a rate of 10 C./min.

[0088] Because of the favorable chemical stability of TiO.sub.2 in organic solvents, its strong metal-support interactions, and its acid-base properties, the Pt/TiO.sub.2 system was explored further with different process conditions. The addition of ethanol as a co-solvent was also evaluated and improved the yields of the 2-EEMPA-CHO intermediate and methanol and decreased the yields of side products, CO, and methane (Table 5, entry 4). However, from the economic feasibility point of view, it is beneficial to avoid using ethanol as the co-solvent in the system. Because ethanol used for CO.sub.2 conversion needs to be separated from the conversion products as well as from the carbon capture solvent, before recycling the carbon capture solvent to the CO.sub.2 absorber. These separations are energy- and capital-intensive involving large distillation columns, big reboilers, and additional process units to break azeotropic between ethanol and water by-product. At low reaction temperatures (e.g., 150 C.) and with short reaction times, methanol was formed with high selectivity, and 100% selectivity toward CN bond cleavage was observed (Table 5, entries 5 and 7). Table 5, entry 5 clearly shows that N-methylation and methanol formation do not occur in parallel with Pt/TiO.sub.2-instead, the methanol is likely acting as an N-methylation source. Thus, by avoiding the longer contact time between the methanol and catalyst, N-methylation can be avoided. On the other hand, at lower H.sub.2 pressure, the methanol yield and CN bond cleavage selectivity were decreased (Table 5, entry 6). The commonly employed post-combustion solvent 30 wt % MEA was also evaluated for the hydrogenation of captured CO.sub.2 with a Pt/TiO.sub.2 catalyst (Table 5, entry 8). .sup.1H NMR analysis revealed the formation of mostly MEA-formate, MEA-N-CHO species, and several MEA decomposition products (FIG. 8). This shows that the current approach of combined capture and conversion to methanol is not practical when using the conventional MEA solvent, in large part because the reaction involves elimination of water, and the formation of water is hindered in aqueous solution (FIG. 1).

TABLE-US-00005 TABLE 5 Hydrogenation of captured CO.sub.2 in the presence of Pt-supported catalysts using batch reactor system. CN CO.sub.2 Product selectivity (%) Methanol cleavage conv. EEMPA- EEMPA Yield selectivity Entry Catalyst (%) CO CH.sub.4 NCHO NMe Methanol (%) (%) 1 5 wt % Pt/CeO.sub.2 29.7 49.5 3.3 11.4 11.4 24.4 7.2 68.0 2 5 wt % Pt/TiO.sub.2 29.1 31.9 19.8 9.0 12.3 27.0 7.9 68.7 3 5 wt % Pt/SiO.sub.2 23.9 77.4 0.0 15.3 7.3 0.0 0.0 0.0 4.sup.a 5 wt % Pt/TiO.sub.2 42.4 15.6 7.8 37.7 11.7 27.2 11.5 69.8 5.sup.b 5 wt % Pt/TiO.sub.2 11.5 35.8 25.6 traces traces 38.7 4.5 100.0 6.sup.d 5 wt % Pt/TiO.sub.2 15.9 0.9 25.9 18.1 26.4 28.6 4.5 52.0 7.sup.e 5 wt % Pt/TiO.sub.2 12.2 25.5 22.4 15.0 traces 37.1 4.5 100.0 8.sup.f 5 wt % Pt/TiO.sub.2 44.7 5.8 1.6 38.1 5.9 7.6 3.4 56.5 9.sup.c 5 wt % Pt/TiO.sub.2 19.3 29.8 16.9 10.6 10.1 32.6 6.3 76.4 Conditions: catalyst = 200 mg, 170 C., EEMPA-5 g (CO.sub.2 loaded EEMPA used, 6 wt % CO.sub.2 loading), initial P(H.sub.2) = 60 bar, time = 12 h, .sup.aethanol, .sup.b3 h, .sup.c10 wt % CO.sub.2, .sup.d30 bar H.sub.2, .sup.e150 C., .sup.f30 wt % MEA was used as a capture solvent; mostly MEA-formate and MEA-N-formamide species were observed; MEA decomposition products were also observed under the reaction conditions.

[0089] In additional batch reactor studies, the TiO.sub.2 support was screened with different metals such as Ni, Ru, Cu, and Pd to understand the role of Pt in selective CN bond cleavage (Table 6). In the reactions with Ni and Ru, methane was formed with high selectivity and no methanol was observed (Table 6, entries 2 and 3). To the best of our knowledge, this is the first example of methane formation from captured CO.sub.2 using a non-noble metal catalyst in the presence of a capture solvent. No methanol was observed in the presence of a Cu/TiO.sub.2 catalyst, but only N-methylation was observed via undesired CO bond cleavage (Table 5, entry 4, also shown in Table 1, entry 6). High Cu content on the TiO.sub.2 support could have limited the availability of the TiO.sub.2 support for the CN cleavage selectivity. It is also important to note that low Cu content (5 wt %) in Cu/CeO.sub.2 catalyst was not sufficient to hydrogenate the EEMPA-CHO intermediate (Table 1, entry 5).

[0090] When Pd was used in place of Pt, the Pd/TiO.sub.2 was less active for the final formamide hydrogenation step (Table 3, entry 5) because Pd has a low concentration of hydrogen atoms on

[0091] the surface compared to Pt..sup.[24] Therefore, the results in Tables 5 and 6 clearly show that the combination of Pt and TiO.sub.2 or CeO.sub.2 supports is best suited for methanol production with reduced or negligible deactivation of the capture solvent.

[0092] Operando .sup.13C NMR was performed with .sup.13C-enriched CO.sub.2 in the presence of a Pt/TiO.sub.2 catalyst to understand the reaction pathway in the condensed phase and confirm the absence of N-methylation. The NMR analysis showed .sup.13CO, 2-EEMPA-.sup.13CHO, .sup.13CH.sub.3OH, and .sup.13CH.sub.4 as predominant species at 183.1, 164.4, 49.1, and 11 ppm, respectively, at 170 C. Simultaneous formation of all these species suggests that methanol can form via both CO and N-formamide intermediates. CO could also form from the decarbonylation of methanol. It is very important to note that no detectable amount of the undesired 2-EEMPA-.sup.13CH.sub.3 species was observed, unlike the Cu/ZnO/Al.sub.2O.sub.3 catalyst under similar reaction conditions (FIG. 6 vs. FIG. 10).

TABLE-US-00006 TABLE 6 Hydrogenation of captured CO.sub.2 in the presence of metals with TiO.sub.2 supports using batch reactor system. CN CO.sub.2 Product selectivity (%) Methanol cleavage Exp. conv. EEMPA- EEMPA Yield selectivity Entry No. Catalyst (%) CO CH.sub.4 NCHO NMe Methanol C.sub.2+ (%) (%) 1 274 5 wt % Pt/TiO.sub.2 29.1 31.9 19.8 9.0 12.3 27.0 0 7.9 68.7 2 287 35 wt % Ni/TiO.sub.2 77.9 0.0 91.4 6.4 0.0 0.0 2.2 7.2 68.0 3 300 5 wt % Ru/TiO.sub.2 >99 0.0 >90 0.0 0.0 0.0 >10 0.0 4 281 35 wt % Cu/TiO.sub.2 15.7 5.6 0.0 76.6 17.8 0.0 0.0 0.0 0.0 5 273 5 wt % Pd/TiO.sub.2 19.9 3.7 16.2 80.1 0.0 0.0 0.0 Conditions: catalyst = 200 mg, 170 C., EEMPA-5 g (CO.sub.2 loaded EEMPA used, 6 wt % CO.sub.2 loading), initial P(H.sub.2) = 60 bar, time = 12 h

[0093] The most promising catalyst formulation Pt/TiO.sub.2 identified in batch reactor studies was then evaluated under continuous-flow operation for a range of operating temperatures and space velocities using CO.sub.2 captured in neat 2-EEMPA solvent (Table 7). When operating at 140 C., the CO.sub.2 conversion was very low (2%) (Table 7, entry 1). However, the catalyst was highly selective toward methanol, with 93% selectivity. Interestingly, the remaining product was primarily propanol, with 7% selectivity. At higher temperatures (170 and 190 C.), ethanol and smaller amounts of butanol were also detected (Table 7, entries 2-8). While the mechanism for their formation is not yet clear, we can learn from decades of research on higher alcohol synthesis from the hydrogenation of CO and CO.sub.2..sup.[25.26] For example, the synergistic effects between metal nanoparticles and the underlying TiO.sub.2 support, especially the anatase crystal phase with abundant oxygen vacancies, have been reported to facilitate ethanol formation from CO.sub.2 and H.sub.2..sup.[27] Thus, this is a very important finding because the production of higher alcohols from syngas and/or CO.sub.2 has been the subject of significant research in the area of conventional thermochemical catalysis. Furthermore, no CO or CO.sub.2 was observed in the gas phase for any of the conditions evaluated. Confirmation that the reaction is primarily occurring in the condensed phase is significant, because any loss of carbon in the form of gas-phase CO or CO.sub.2 would require additional energy and cost for recapture and conversion.

[0094] Also, when the operating temperature was increased from 140 to 190 C. (Table 7, entry 5), the CO.sub.2 conversion modestly increased from 2% to 12%. However, the methanol selectivity was reduced from 93% to 78%. When higher alcohols were formed in addition to methanol, the generation of methane with 15% selectivity was also observed. While methane is considered an undesired side product in alcohol production reaction, the production of methane could have its advantages as a CO.sub.2-neutral fuel. When operating at 190 C., the space velocity was decreased by a factor of 10 and the conversion increased from 12% to 86% (Table 5, entries 4 and 6). However, methanol selectivity decreased from 78% to 52% because of increasing methane and ethane formation.

[0095] Catalytic performance results in Table 7 (entries 6-8) show how the activity of Pt/TiO.sub.2 decreases over time (CO.sub.2 conversion steadily drops from 85.7% to 65.2% over 80 h of reaction). To understand possible underlying deactivation mechanisms, we performed postmortem characterization of the catalyst used in this reaction using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), temperature-programmed oxidation with mass spectrometry (TPO-MS), X-ray powder diffraction (XRD), and inductively coupled plasma (ICP) and compared the results with those of the fresh catalyst. DRIFTS of the fresh and spent catalysts showed the presence of adsorbed water (FIG. 14). The spent catalyst also showed alkane CH stretching bands between 3000 and 2800 cm.sup.1, which corresponds to the capture solvent (EEMPA). The main infrared features of the spent catalyst are the presence of CO adsorbed on Pt and of carbonate-like species in different adsorption modes (note that these carbonate-like species are also present in the fresh catalyst sample). The spent catalyst showed the presence of a terminal PtCO (2116 cm.sup.1) and a weak band at 1873 cm.sup.1 for bridged PtCO. Multiple bands appeared in the carbonate region between 1700 and 1200 cm.sup.1, corresponding to the carbonates, carbamates, and bicarbonates..sup.[28] Both species (CO and carbonates) have been described in the literature as reasons for metal/support catalyst deactivationin the case of CO due to a reduction of active sites on the Pt surface and in the case of carbonates due to a reduced number of interface PtTiO.sub.2 active sites where they are preferentially formed..sup.[28] Physical changes to the catalyst (e.g., sintering/leaching of platinum particles) cannot be discarded, despite the mild conditions used. There was no appreciable change in the Pt dispersion between the fresh and spent catalysts based on the CO chemisorption (Table 8), suggesting no Pt sintering during the reaction. The presence of organic residue on the spent catalyst makes ICP (for Pt) and elemental analysis (C, H, N, S) quantification difficult or inconclusive. The Pt content of the fresh and spent Pt/TiO.sub.2 catalysts was 5.6% and 4.5%, respectively. The capture solvent absorbed on the spent catalyst could be the reason for the low Pt content (and high C, H, N content) in the spent catalyst. The Pt crystallite size as determined by XRD remained below the detection limit. Further, XRD did not indicate any change in the TiO.sub.2 support predominantly anatase phase after reaction. The XRD and elemental analysis (CHNSO) results are presented in FIG. 11.

TABLE-US-00007 TABLE 7 Hydrogenation of captured CO.sub.2 over Pt/TiO.sub.2 catalyst over a range of operating temperatures and space velocities using a continuous flow reactor system. Reaction CO.sub.2 temperature Conversion WHSV TOS Selectivity [mol C %] Entry [ C.] [%] g.sub.CO2/g.sub.cat/h [h] MeOH EtOH PrOH BuOH CH.sub.4 C.sub.2H.sub.6 1 140 2.2 0.15 92.7 0.0 7.3 0.0 0.0 0.0 2 170 7.7 0.15 66.5 4.3 2.5 0.7 26.0 0.0 3 170 29.1 0.015 57.0 4.5 0.8 1.4 26.7 8.7 4 190 11.8 0.15 78.0 4.3 0.0 2.5 15.1 0.0 5 190 26.9 0.075 63.6 4.6 0.2 1.9 26.4 3.3 6 190 85.7 0.015 40 51.5 9.7 0.6 1.9 27.1 9.3 7 190 75.9 0.015 60 50.2 8.6 0.7 2.0 29.2 9.3 8 190 65.2 0.015 80 46.0 8.0 1.1 4.7 29.8 10.5 Liquid feed: captured CO.sub.2 in EEMPA solvent (5 wt % CO.sub.2) over 5 wt % Pt/TiO.sub.2 catalyst. Reaction conditions: 1.0 g catalyst, 870 psig; Gas feed: (0.05, 0.025, 0.005 mL/min). 38 sccm H.sub.2, 5 sccm N.sub.2. Change in WHSV is achieved by changing the liquid feed flow. Catalyst was pretreated in situ overnight at 120 C. under reducing flow (50 sccm 10% H.sub.2 in N.sub.2).

TABLE-US-00008 TABLE 8 Pt dispersion characterization of 5 wt % Pt catalysts using CO pulse chemisorption. CO Chemisorption CO Chemisorption Entry Catalysts Surface Pt (mol/g) Pt dispersion 1 5 wt % Pt/TiO.sub.2 72.5 28.6% 2 5 wt % Pt/TiO.sub.2 (spent) 74.0 28.9% 3 5 wt % Pt/CeO.sub.2 63.4 25.1% 4 5 wt % Pt/SiO.sub.2 77.35 30.2% Analytical conditions: 100 mg of sample was purged under flowing He (25 sccm) for 10 min. Samples were pretreated in situ at 200 C. with 10% O.sub.2/He for 2 h, followed by reduction at 200 C. with 10% H.sub.2/N.sub.2 for 20 min, He purge at 200 C. for 10 min, then cooled to 40 C. for CO chemisorption.

[0096] The TPO-MS analysis of the fresh Pt/TiO.sub.2 catalyst showed signals for the loss of water between 150 and 500 C. (FIG. 15). The spent catalyst showed the presence of water, CO.sub.2, and a small amount of CO. The metal-bound CO is possibly formed from the rWGS reaction. The following could be potential CO.sub.2 sources: 1) the 2-EEMPA carbamate species bound to the Pt, which can release CO.sub.2 with an increase in temperature (2-EEMPA-CO.sub.2 to 2-EEMPA+CO.sub.2), 2) surface bicarbonate species formed upon the reaction of CO.sub.2 or 2-EEMPA carbamate with water. The bicarbonate species can decompose to produce CO.sub.2, water, and carbonate species (2HCO.sub.3 to CO.sub.2+H.sub.2O+CO.sub.3.sup.2), 3) oxidation of adsorbed organic species such as HCO.sub.2.sup., 2-EEMPA, 2-EEMPA-CHO and 2-EEMPA-CH.sub.3. The concurrent formation of water and CO.sub.2 points to the oxidation of these organic species, 4) oxidation of adsorbed CO under TPO conditions (10% O.sub.2/He), the surface-bound CO species could oxidize to give CO.sub.2 (2CO+O.sub.2 to 2CO.sub.2). In addition, the TPO profile of the spent catalyst (FIG. 15) shows that desorption and oxidation of adsorbed species occur at moderate temperatures (<300 C.) and that CO gets desorbed at temperatures slightly higher than the reaction temperature (190 C.). This relatively strong (and extended) CO adsorption is consistent with literature reports, which indicate this as the main reason for Pt deactivation at these mild reaction temperatures (<200 C.) and for weaker COPt adsorption at higher temperatures..sup.[28] Solvent adsorbed on the catalyst (3000-2800 cm.sup.1 infrared bands in FIG. 14) decomposes also at moderate oxidation temperatures (NO peak max at 290 C. in FIG. 15). Both DRIFTS and TPO-MS analyses suggest that CO and carbonates are blocking the active sites of the spent catalyst. However, operando .sup.13C MAS-NMR showed only the presence of metal-bound CO under the reaction conditions (at 170 C.) and that the carbonate/carbamate/bicarbonate species are formed only at room temperature (FIG. 15). CO-TPD was performed on the CO chemisorbed Pt/TiO.sub.2 catalyst to further evaluate strong CO adsorption. CO-TPD results suggest that CO is strongly bound to the catalyst surface (COPt) even at the reaction temperature of 190 C. (FIG. 12). Overall, based on DRIFTS, in situ .sup.13C MAS-NMR, and TPO-MS, we conclude that the catalyst is most likely poisoned by the strong adsorption of CO on Pt. Regeneration/reactivation is possible at relatively moderate oxidation/desorption temperatures.

References

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