Selective hydrogenation of acetylene over Pd/Fiberglass catalysts: Kinetic and isotopic studies

Abstract

In this study two palladium fiberglass catalysts differing in the location of Pd particles have been synthesized and characterized in detail by means of XPS and HRTEM/STEM. In the first catalyst prepared using H2PdCl4 as a precursor palladium deposits on the external surface of glass fibers, whereas in the second catalyst prepared using ion exchange of [Pd(NH3)4]2+ cations with the glass protons palladium is located in the subsurface layers of glass. It was clearly shown by SSITKA (steady-state isotopic transient kinetic analysis) with the use of doubly labeled acetylene 13C2H2 that gas-phase ethylene is not involved in the selective hydrogenation of acetylene over the second catalyst in contrast to the first one where ethylene is also hydrogenated into ethane. This fact was explained by an ability of glass to absorb predominantly such readily polarizable molecules like acetylene, but not ethylene. As a result, the fiberglass catalyst where Pd clusters are confined in the glass matrix demonstrates high selectivity (ethylene increment ca. 60%) at complete conversion of acetylene. So, Pd fiberglass catalysts were shown to be very promising for the selective hydrogenation processes.