The Effect of Sn Content in a Pt/KIT-6 Catalyst Over its Performance in the Dehydrogenation of Propane

Abstract

Propylene is one of the most important commodity chemicals. Its future demand is expected to exceed its production. Alternative routes to obtain this product need to be implemented. Dehydrogenation of propane assisted with catalyst is a promising route to meet demands. The Pt and Cr supported catalysts are amongst the most effective possibilities. However, Pt catalysts are preferred over Cr due to the toxic nature of Cr species. Despite the high performance of the Pt catalysts, they deactivate during reaction, mainly due to coke deposits blocking the active site and/or pores. This effect can be reduced with a support having high connectivity and surface area, like KIT-6. In this work the mesoporous silica KIT-6 was employed as support in a series of Pt-Sn catalysts. The influence of adding or increasing the weight % of Sn to Pt catalyst was studied. There were species of SnO2 and metallic Pt in the fresh catalysts. After reaction, it was found that in the catalysts with the lowest wt % of Sn (0.5), there were metallic Pt and a Pt-Sn alloy. In the rest of the used catalysts (containing 1.0, 1.5 and 2.0 wt % of Sn) the only detected specie was the Pt-Sn alloy. In the two most active catalysts (having 0.5 and 1.5 wt % of Sn), it was observed a difference of three times the quantity of coke deposited on the surface. The catalysts containing the highest coke deposits maintained its activity due to the high connectivity of the support.

A Comprehensive Study of Coke Deposits on a Pt-Sn/SBA-16 Catalyst during the Dehydrogenation of Propane

“…On the other hand, the same XPS peak position is observed at 284.7 eV for all the catalysts (Figure 11b-e), with peak intensity growth indicating the formation of carbon and without significant shifting in the peak signal [41,42]. From XPS and previous studies of our group [11,12], it can be inferred that there is a Pt-Sn alloy in which the carbon was deposited as the TOS increased. Besides, the excess of Sn is in an oxide state, Sn (II) oxide and Sn (IV) oxide.…”

“…This is not expected given that the exposed Pt is reducing with sintering then the conversion should decrease. Maybe during this sintering some of the coke Figure 13 illustrates the TEM images and their corresponding particle size distribution for the 0.5-Pt-1-Sn/SBA-100 catalyst with different TOS; the average particle size of the Pt alloy [11,12] in each case is listed in Table 4. For the reduced sample ( Figure 13A, 0 min on stream), the particle exhibited a good distribution and the lowest particle size (Figure 13B).…”

“…Several reports in the technical literature shed some light in the current understanding of ways of dealing with catalyst deactivation, for example, by adding a second metal to the Pt catalyst [6], using other supports rather than the typically employed Al 2 O 3 [7], modifying the Pt particle size [8], and others [9,10]. The incorporation of a highly connected support is a less commonly implemented methodology to address coke deposits and the subsequent catalyst deactivation [11,12]. Highly ordered mesoporous materials with a three-dimensional porous structure [13], similar to KIT-6 and SBA-16, can be incorporated as support in the catalyst yielding good dispersion of the active phase during catalyst synthesis thereby enhancing diffusion of both, species involved in the main reaction and the coke precursor species.…”