Revisiting hydrogen spillover in Pt/LTA: Effects of physical diluents having different acid site distributions

Abstract

Historically, Pt/LTA (e.g., Pt/NaA) has often been used as a model catalyst for studying the catalytic functions of hydrogen spillover (H spillover). Notably, none of the works reported appreciable catalytic activities for Pt/LTA alone, while markedly enhanced activities were reported after physical dilution with some acidic oxides. It was often speculated without experimental evidence that activated hydrogen generated from Pt/LTA can migrate to the diluents surface ("inter-particular" H spillover) where organic reactants can react with spilt-over hydrogen. In this work, we carefully studied benzene hydrogenation activities of Pt/NaA and its decationized form (Pt/HA), before and after the physical dilution with various metal oxides possessing different Lewis and Bronsted acidity. The originally negligible activity of Pt/NaA increased significantly after mixing with various acidic oxides. The physical dilutions, however, resulted in a significant alteration of Pt/NaA structure due to solid-state H+ exchange, which made the catalytic interpretation vague. In contrast, Pt/HA structure did not change after the dilutions, and thus could be used as an ideal catalytic model system for studying inter-particular H spillover. The catalytic results showed that Al-rich metal oxides with abundant Lewis acid sites are effective for enhancing the catalytic activity.