Elucidation of hydrogen spillover phenomenon on solid acid catalysts

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Solid acid site is the catalytic active site for the isomerization, hydrocracking, disproportionation of hydrocarbons. The problem in these kinds of reaction is the carbon deposition on the solid acid catalyst which are formed by the polymerization, and this deactivates the catalyst. In the case that noble metals are introduced to the solid acid catalyst by supporting or physically mixing, the deactivation is considerably inhibited. It has been reported that the cofeed of hydrogen is very effective to the inhibition of the deactivation. The effect of hydrogen has been expalined by the hydrogen spillover phenomenon. Hydrogen molecule dissociates on metal surface and spills over to the acid site. The spilled over hydrogen regenerates the acid site and supplies the hydride to the hydrocarbon reaction intermediate. We have proposed the reaction mechanism on the basis of the spillover effect. In this study, we observed the behavior of adsorbed pyridine on the acid site under hydrogen flowing by means of FTIR.From the comparison between zeolite supported Pt catalyst and the physical mixture of zeolite with Pt/SiO_2 catalyst, it was found that spillover hydrogen promotes the desorption of adsorbed pyridine on Lewis acid site. This result suggests the formation of hydride as the spillover hydrogen.