Supported PtZn intermetallic alloy catalyst, method for preparing the same and application thereof

Abstract

The present application discloses a supported PtZn intermetallic alloy catalyst, a method for preparing the same and application thereof. The catalyst uses SiO.sub.2 as a support and Zn as a promoter, and a small amount of active component Pt is supported; the weight percentage of Pt is 0.025%-1%, and the weight percentage of Zn is 0.025%-1.7%, a co-impregnation method is adopted in preparation, the SiO.sub.2 support is impregnated in aqueous solution of chloroplatinic acid and zinc nitrate, and then drying and high-temperature reduction are performed to obtain a PtZn/SiO.sub.2 catalyst. The catalyst has the advantages of high activity, high stability, low price and low toxicity. The catalyst provided by the present application is applicable to preparation of alkene through short-chain alkane dehydrogenation, in particular to preparation of propylene through propane dehydrogenation in a hydrogen atmosphere. Under high-temperature conditions, the dehydrogenation activity is very high, the propylene selectivity can reach more than 90%, the stability is good, and the amount of used Pt is small, the utilization rate is high, and it is cheaper than industrial Pt series catalysts.

Claims

1. A process for the dehydrogenation of an alkane to prepare an alkene, comprising reacting the alkane in the presence of a supported PtZn intermetallic alloy catalyst to produce the alkene, wherein the alkane comprises ethane, propane, and/or butane; wherein the supported PtZn intermetallic alloy catalyst comprises Pt as an active component and Zn as a promoter; wherein said Pt and Zn are supported on a support and form an atomically ordered intermetallic alloy; and wherein, based on the weight of the support in the catalyst, the weight percentage of Pt is no more than 1 wt %, and the weight percentage of Zn is no more than 1.7 wt %.

2. The process according to claim 1, wherein the alkene is propylene and the alkane is propane; and wherein the dehydrogenation of the alkane is carried out according to the following steps: tableting the supported PtZn intermetallic alloy catalyst into a granular catalyst with a mesh size of 20-40 meshes; putting the obtained granular catalyst into a fixed bed reactor, feeding with nitrogen, and then heating the temperature to a pretreatment temperature of 500-700° C.; performing pretreatment with hydrogen, maintaining the temperature at the pretreatment temperature for 0.5h-1h, and then tuning the temperature to a reaction temperature of 500-650° C.; and performing reaction with a reaction gas comprising propane and hydrogen; wherein the molar ratio of hydrogen to propane is (0-2):1, nitrogen is an equilibrium gas, the total gas amount is kept unchanged, and the reaction space velocity based on propane is 1-5h.sup.−1.

3. The process according to claim 1, wherein the weight percentage of Pt is 0.025 wt %-1 wt %.

4. The process according to claim 1, wherein the weight percentage of Zn is 0.025 wt %-1.5 wt %.

5. The process according to claim 1, wherein the support is one selected from the group consisting of silicon dioxide, molecular sieve, zeolite, and aluminum oxide.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates an AC-HAADF-TEM photo of a SiO.sub.2 supported PtZn intermetallic alloy catalyst prepared in embodiment 1 according to the present application.

(2) FIG. 2 illustrates an XRD spectrum of a SiO.sub.2 supported PtZn intermetallic alloy catalyst prepared in embodiment 1 according to the present application.

(3) FIG. 3 illustrates an activity test curve chart of PtZn intermetallic alloy catalysts supported by respectively using SiO.sub.2 and Al.sub.2O.sub.3 in embodiment 1 according to the present application, wherein a curve above a chemical formula corresponds to propylene selectivity and a curve below the chemical formula corresponds to propane conversion rate.

(4) FIG. 4 illustrates a test curve chart of influence of different Zn weight percentages on catalytic activity, in the embodiments of the present application wherein curves at an upper position correspond to propylene selectivity and curves at a lower position correspond to propane conversion rate.

(5) FIG. 5 illustrates a test curve chart of influence of different Pt contents on catalytic activity in the embodiments of the present application, wherein curves at an upper position correspond to propylene selectivity and curves at a lower position correspond to propane conversion rate.

(6) FIG. 6 illustrates a test curve chart of influence of different pre-reduction temperature on catalytic activity in the embodiments of the present application, wherein curves at an upper position correspond to propylene selectivity and curves at a lower position correspond to propane conversion rate.

(7) FIG. 7 illustrates a test curve chart of influence of different reaction temperature on catalytic activity in the embodiments of the present application, wherein curves at an upper position correspond to propylene selectivity and curves at a lower position correspond to propane conversion rate.

(8) FIG. 8 illustrates a test curve chart of influence of different propane space velocities on catalytic activity in the embodiments of the present application, wherein curves at an upper position correspond to propylene selectivity and curves at a lower position correspond to propane conversion rate.

(9) FIG. 9 illustrates a test curve chart of influence of different propane/hydrogen ratios on catalytic activity in the embodiments of the present application, wherein curves at an upper position correspond to propylene selectivity and curves at a lower position correspond to propane conversion rate.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

(10) The present application will be further described below in detail through specific examples. The following examples can allow those skilled in the art to more comprehensively understand the present application, rather than to limit the present application in any form.

Embodiment 1

(11) Step (1) 0.0021 g of H.sub.2PtCl.sub.6 and 0.078 g of Zn(NO.sub.3).sub.2.6H.sub.2O were dissolved in 4 ml deionized water to prepare a solution;

(12) Step (2) 1.0000 g of SiO.sub.2 (or Al.sub.2O.sub.3) was impregnated in the prepared solution, ultrasonic treatment was performed for 0.5 h, and drying was performed for 12 h at room temperature, and drying was performed at 100° C. until completely dried;

(13) Step (3) the solid obtained in the step (2) was reduced for 1 h at 600° C. to obtain a PtZn/SiO.sub.2 (or PtZn/Al.sub.2O.sub.3) catalyst. Based on the weight of the support in the catalyst, the weight percentage of Pt was 0.1 wt % and the mass percentage of Zn was 0.17 wt %;

(14) Step (4) the prepared SiO.sub.2 (or Al.sub.2O.sub.3) supported intermetallic catalyst was tableted to obtain a 20-mesh to 40-mesh granular catalyst;

(15) Step (5) the tableted SiO.sub.2 (or Al.sub.2O.sub.3) supported intermetallic granular catalyst was contained into a fixed bed reactor, nitrogen was fed, and the temperature was increased to 600° C.; hydrogen was fed for pretreatment, and the temperature was kept for 1 h at 600° C.; the reaction temperature was 600° C., the weight hourly space velocity of propane was 4 h.sup.−1, the molar ratio of hydrogen to propane in the reaction gas was 1:1 and the equilibrium gas was nitrogen.

(16) The activity of the catalyst was expressed by propane conversion rate, propylene selectivity and deactivation rate. The propylene selectivity and deactivation rate were calculated as follows:

(17) Selectivity:

(18) $\mathrm{Sel}\left(\%\right)=\frac{{.Math.F_{C_3{H}_8}]}_{\mathrm{out}}}{{.Math.F_{C_3{H}_8}]}_{\mathrm{in}}-{.Math.F_{C_3{H}_8}]}_{\mathrm{out}}}\times 100$

(19) Conversion rate:

(20) $\mathrm{Con}\left(\%\right)=\frac{{\left[F_{C_3{H}_8}\right]}_{\mathrm{in}}-{.Math.F_{C_3{H}_8}]}_{\mathrm{out}}}{{.Math.F_{C_3{H}_8}]}_{\mathrm{in}}}\times 100$

(21) Deactivation rate:

(22) $k_d=\left[\ln \left(\frac{1-X_{\mathrm{final}}}{X_{\mathrm{final}}}\right)-\ln \left(\frac{1-X_{\mathrm{initial}}}{X_{\mathrm{initial}}}\right)\right]/t$

(23) where [F.sub.C.sub.3.sub.H.sub.8].sub.in represents volume flow rate of propane at a reactor inlet, [F.sub.C.sub.3.sub.H.sub.8].sub.out and [F.sub.C.sub.3.sub.H.sub.6].sub.out respectively represent gas volume flow rates of propane and propylene at a reactor outlet, X.sub.initial and X.sub.final respectively represent propane conversion rates at beginning and end of reaction.

(24) FIG. 1 illustrates an AC-HAADF-TEM photo of the PtZn/SiO.sub.2 catalyst prepared in the Embodiment 1, from which it can be seen that Pt and Zn atoms are arranged in order in a spaced manner, while the PtZn monoatomic alloy is attached to the surface of the SiO.sub.2 support. FIG. 2 illustrates an XRD curve chart of the PtZn/SiO.sub.2 catalyst prepared in the Embodiment 1, showing the crystal phase structure of the PtZn intermetallic alloy.

(25) Reaction products were analyzed online by adopting gas chromatography. A relationship between propane conversion rate and propylene selectivity as the reaction time is illustrated in FIG. 3. It can be seen that, for the catalyst using silicon dioxide as the support, the propane conversion rate is 48.1% at the beginning and 47.8% after 10 h, the deactivation rate is only 0.0028 h.sup.−1, and the propylene selectivity always remains at a high level (>94%); for the catalyst using aluminum oxide as the support, the propane conversion rate and the propylene selectivity are not as good as the former.

Embodiment 2

(26) The method in the embodiment 1 was used for preparation and reaction, and the difference was only that the weight of zinc nitrate (Zn(NO.sub.3).sub.2.6H.sub.2O) in step (1) was 0.026 g; based on the weight of the support, the weight percentage of Zn in the obtained catalyst was 0.06 wt %.

Embodiment 3

(27) The method in the embodiment 1 was used for preparation and reaction, and the difference was only that the weight of zinc nitrate (Zn(NO.sub.3).sub.2.6H.sub.2O) in step (1) was 0.234 g; based on the weight of the support, the weight percentage of Zn in the obtained catalyst was 0.5 wt %.

Embodiment 4

(28) The method in the embodiment 1 was used for preparation and reaction, and the difference was only that the weight of H.sub.2PtCl.sub.6 in step (1) was 0.0011 g; based on the weight of the support, the weight percentage of Pt in the obtained catalyst was 0.05 wt %.

Embodiment 5

(29) The method in the embodiment 1 was used for preparation and reaction, and the difference was only that the weight of H.sub.2PtCl.sub.6 in step (1) was 0.007 g; based on the weight of the support, the weight percentage of Pt in the obtained catalyst was 0.3 wt %.

Embodiment 6

(30) The method in the embodiment 1 was used for preparation and reaction, and the difference was only that the reduction temperature in step (3) was 300° C.

Embodiment 7

(31) The method in the embodiment 1 was used for preparation and reaction, and the difference was only that the reaction temperature in step (5) was 520° C.

Embodiment 8

(32) The method in the embodiment 1 was used for preparation and reaction, and the difference was only that the reaction temperature in step (5) was 550° C.

Embodiment 9

(33) The method in the embodiment 1 was used for preparation and reaction, and the difference was only that the reaction temperature in step (5) was 620° C.

Embodiment 10

(34) The method in the embodiment 1 was used for preparation and reaction, and the difference was only that the weight hourly space velocity of propane in step (5) was 9.5 h.sup.−1.

Embodiment 11

(35) The method in the embodiment 1 was used for preparation and reaction, and the difference was only that the ratio of hydrogen to propane in step (5) was 0.

Embodiment 12

(36) The method in the embodiment 1 was used for preparation and reaction, and the difference was only that the ratio of hydrogen to propane in step (5) was 0.5.

Embodiment 13

(37) The method in the embodiment 1 was used for preparation and reaction, and the difference was only that the ratio of hydrogen to propane in step (5) was 2.

(38) For the results of the above embodiments, the activity data at the beginning and at 10 h of the reaction were compared. The test conditions and methods were the same as those in the embodiment 1 (using silicon dioxide as support) to investigate the influence of different parameters on the reaction performance of the catalyst.

(39) (1) For the influence of the weight percentage of Zn (based on the weight of the support in the catalyst) on the reaction activity of the PtZn/SiO.sub.2 catalyst, refer to FIG. 4. The reaction conditions are the same as those in the embodiments 1, 2 and 3. It can be seen from FIG. 4 that when the weight percentage of Zn is 0.06-0.5 wt %, the catalyst achieves high stability and activity at the same time. The propane conversion rate at the beginning is about 48%, the selectivity is about 96%, and the deactivation rate is about 0.0028 h.sup.−1. The reaction conditions are the same as those in the embodiments 1, 4 and 5.

(40) (2) For the influence of the weight percentage of Pt (based on the weight of the support in the catalyst) on the reaction activity of the PtZn/SiO.sub.2 catalyst, refer to FIG. 5. The reaction conditions are the same as those in the embodiments 1, 4 and 5. It can be seen from FIG. 5 that when the weight percentage of Pt is 0.05 wt %, the activity is good but the stability is poor. When the weight percentage of Pt is moderate (0.1 wt %), the catalyst can achieve very good activity and stability at the same time. The propane conversion rate at the beginning is 48%, the selectivity is 95%, and the deactivation rate is only 0.014 h.sup.−1.

(41) (3) For the influence of the pre-reduction temperature on the reaction activity of the PtZn/SiO.sub.2 catalyst, refer to FIG. 6. The reaction conditions are the same as those in the embodiments 1 and 6. It can be seen from FIG. 6 that the pre-reduction temperature has an important influence on the reaction activity and selectivity. High-temperature reduction is the necessary condition for the formation of the intermetallic alloy, and the reduction temperature is preferably 600° C.

(42) (4) For the influence of the reaction temperature on the catalytic activity of the PtZn/SiO.sub.2 catalyst, refer to FIG. 7. The reaction conditions are the same as those in the embodiments 1, 7, 8 and 9. It can be seen from FIG. 7 that, with the increase of the reaction temperature, the propane conversion rate increases gradually, but the propylene selectivity decreases, and the best conversion rate and selectivity are obtained at 600° C.

(43) (5) For the influence of the propane space velocity on the propane dehydrogenation activity, refer to FIG. 8. The reaction conditions are the same as those in the embodiments 1 and 10. It can be seen from FIG. 8 that, with the increase of the propane space velocity, the propane conversion rate decreases, so the optimum space velocity is 4 h.sup.−1.

(44) (6) For the influence of the ratio of propane to hydrogen on the propane dehydrogenation activity, refer to FIG. 9. The reaction conditions are the same as those in the embodiments 1, 11, 12 and 13. It can be seen from FIG. 9 that, with the increase of H.sub.2:C.sub.3H.sub.8, the propane conversion rate decreases slightly, but the propylene selectivity increases significantly, which indicates that H.sub.2 partial pressure has a significant influence on the propane dehydrogenation reaction, and the optimum ratio of propane to hydrogen is 1.

(45) The preparation of the catalyst in the present application can be realized by adjusting the process parameters according to the content of the present application, and the performance basically consistent with the examples is shown in the tests. The present application has been exemplarily described above. It should be noted that, without departing from the core of the present application, any simple deformation, modification or equivalent replacement by those skilled in the art without contributing any inventive labor should fall into the scope of protection of the present application.