Increased Catalytic Activity Caused by Local Destruction of Linear Zeolite Channels: Effect of Reduction Temperature on Heptane Conversion over Platinum Supported in H-Mordenite

The conversion of n-heptane was studied on Pt/HMor. The response of catalytic activity and isomerization selectivity to reduction temperature and metal dispersion is contrary to that known for Pt on amorphous supports or on zeolites with three-dimensional pore systems: samples reduced at 500°C. though having distinctly lower Pt dispersion, are about twice as active as samples reduced at 350°C. It is shown that for strictly one-dimensional pores the conditions of single file diffusion are fulfilled; products formed deep in the pores are unable to escape. Reduction at 500°C produces Pt particles large enough to locally destroy the zeolite; this transformation of one-dimensional into three-dimensional pores removes the transport restrictions of single file diffusion and increases site accessibility.