A PLATINUM-GALLIUM BASED ALKANE DEHYDROGENATION CATALYST CONTAINING AN OXIDATION PROMOTER

Abstract

A platinum-gallium based catalyst for alkane dehydrogenation is provided with an oxidation promotor in the form of cerium that is added to the catalyst composition to improve the regeneration thereof. The cerium is preferably added to the catalyst composition in an amount from 0.001 to 0.5 wt %.

Claims

1. A catalyst for the dehydrogenation of lower alkanes, whereby the alkanes are dehydrogenated to the corresponding alkenes according to the reaction
C.sub.nH.sub.2n+2<->C.sub.nH.sub.2n+H.sub.2 in which n is an integer from 2 to 5, by feeding the alkane to a catalyst-containing dehydrogenation reactor, wherein the catalyst is based on optionally Si-doped alumina that has been impregnated with gallium and platinum, and cerium in an amount from 0.001 to 0.5 wt % is added to the catalyst as an oxidation promotor together with gallium and platinum, thereby improving the regeneration of the catalyst composition.

2. (canceled)

3. The catalyst according to claim 1, wherein the amount of cerium added to the catalyst composition is between 0.05 and 0.2 wt %.

4. The catalyst according to claim 1, wherein cerium is added as a salt.

5. The catalyst according to claim 1, wherein cerium is added by impregnation together with gallium and platinum.

6. The catalyst according to claim 1, wherein the amount of platinum impregnated into the catalyst composition is up to around 200 ppm.

7. The catalyst according to claim 1, wherein cerium is added as Ce(NO.sub.3).sub.2.6H.sub.2O.

Description

[0023] The invention is illustrated further by the examples which follow. In the examples, reference is made to FIGS. 1 and 2, where

[0024] FIG. 1 illustrates the impact of cerium on the regeneration procedure, and

[0025] FIG. 2 shows the activity of catalysts with and without cerium.

EXAMPLE 1

[0026] This example illustrates the synthesis of a catalyst including the oxidation promotor according to the invention. The synthesis is carried out by co-impregnating approximately 0.1 wt % Ce together with approximately 50 ppm Pt, 1 wt % Ga and 0.2 wt % K on an alumina carrier.

[0027] More specifically, a mixture of 4 g of a 5% Ga solution in HNO.sub.3, 0.2 g of a 0.5 wt % Pt solution (Pt(NH.sub.3).sub.4(HCO.sub.3).sub.2), 0.062 g of Ce(NO.sub.3).sub.2.6H.sub.2O and 0.05 g KNO.sub.3 is diluted with 11 g water. The resulting solution is used to impregnate 20 g of gamma/theta Al.sub.2O.sub.3 (spheres, 1000 C., pore volume 0.75 ml/g). The sample is rolled for 1 hour, dried overnight and calcined at 700 C. for 2 hours with a heating ramp of 4 hours.

[0028] The effect of Ce on the catalyst regeneration is described in the below examples 2 and 3.

EXAMPLE 2

[0029] The impact of cerium on the regeneration is illustrated in FIG. 1. In the experiment leading to FIG. 1, the first PDH cycle was done after regeneration at 630 C., whereas later cycles were done after regeneration at 555 C. The temperature during the PDH was the same in all the cases, more specifically 555 C. A distinct decrease in activity upon recycling at a lower regeneration temperature can be seen for a Pt/Ga catalyst (Catalyst A in FIG. 1). The addition of 0.1% Ce (catalyst A-oxidation promoter in FIG. 1) results in a smaller decrease in activity upon lowering the regeneration temperature. This finding indicates that Ce is able to promote oxidation of the catalyst, and thereby it is possible to regain a larger part of the activity that was lost during the PDH.

EXAMPLE 3

[0030] FIG. 2 shows the activity of catalysts with and without Ce. More specifically, FIG. 2 shows the results from testing 0.75 g of catalyst pellets in a single-pellet string reactor.

[0031] Catalyst B is the reference Pt/Ga catalyst on a carrier calcined at 1000 C. In the first experiment, the catalyst was regenerated every time at 630 C. for 2 hours. With this treatment, the catalyst reached its maximum potential. In the second experiment, the same catalyst was regenerated every time at 630 C. for 30 minutes. It can be seen that the activity is substantially lower in this case.

[0032] In the following experiments 3 to 6, Ce in an amount of 0.05, 0.1, 0.2 or 0.4 wt %, respectively, was co-impregnated with Pt/Ga. The testing was, in all cases, carried out with regeneration at 630 C. for 30 minutes. The performance of the catalyst with 0.05 wt % Ce is significantly better than that of Catalyst B under the same conditions. It actually comes close to the maximum potential activity of Catalyst B which is obtained after regeneration for 2 hours. It seems that although cerium improves the regeneration, it might also lower the maximum potential activity by blocking the active Ga sites. This suggests that ultimately, for the final catalyst, an optimal balance between maximum potential activity and regeneration speed has to be determined.

[0033] The two last experiments were done without any Pt in the catalyst. The second to last catalyst contains 0.1 wt % Ce, whereas the last catalyst contains no Ce. The absence of Pt resulted in a much lower activity, and the addition of Ce to the Ga catalyst without Pt did not improve the activity. The current view is therefore that Pt mainly promotes the dehydrogenation of propane, whereas Ce is promoting the regeneration of the catalyst without having any active role in the PDH step. The addition of cerium also does not have any effect on the selectivity or the oil or coke formation on the catalyst.