(188h) Using Pore Size to Control Selectivity for Acetylene Hydrogenation on Pd@LTA Zeolite Catalysts

Selective hydrogenation of acetylene in ethylene-rich streams is an important industrial reaction. To improve the ethylene selectivity on Pd-based catalysts, we incorporated highly dispersed Pd into 4A, a Linde typeA zeolite with a pore size of ~4 Å, with the assistance of ethylenediamine silane (EDA-Silane). Reaction studies indicated that incorporation of Pd within the zeolite (Pd@4A) resulted in higher ethylene selectivity compared to deposition on the external surface of the zeolite (Pd/4A), even at high conversions near 99%. Pressure decay adsorption measurements indicated that diffusion was markedly faster for acetylene compared to ethylene within the 4A. To test the hypothesis that pore size determined selectivity, Pd@4A zeolites were further modified by variable loadings of NaOH. Physisorption measurements with H₂ indicated that the pore size of 4A could be systematically narrowed by the introduction of NaOH, which enabled higher ethylene selectivity (~80% under 93% acetylene conversion). However, excessive NaOH loading leads to low activity. This strategy provides an alternative way for incorporating metal within the zeolite and an avenue for enhancing the selectivity by tuning the gas affinity onto active side inside the porous material.