Effect of modification on Pd dispersion, acidity, sulfur resistance and catalysis of Pd/Al-MCM-41 zeolite

摘要

A series of Pd catalysts supported on modified Al-MCM-41 zeolite were prepared by impregnation and dimethyl ether synthesis from sulfur-containing syngas over hybrid catalysts. The effect of acid or acid/MxOy (CeO2, ZnO or ZrO2) on the Pd dispersion, acidity, sulfur-resistance and catalysis of a Pd/Al-MCM-41 zeolite was investigated. Acid-modified Pd/Al-MCM-41 zeolite effectively increased the number of moderate acidic sites. However, the Al-MCM-41 zeolite was collapsed due to destruction of the acid on the structure, which decreased the active surface area of the Pd phases. Adding MxOy effectively fixed SO42-, reduced destruction of the catalyst structure and stabilized the effect of acid on the acidity. In addition, the MxOy fixed SO42- effectively, which reduced SO42- by reacting with the overflow hydrogen to generate H2S, thus stabilizing the catalytic activity of Pd. It was found that Pd supported on 0.4 mol L-1 H2SO4/1% ZrO2 modified the stable Al-MCM-41 zeolite and showed excellent CO conversion and DME selectivity as well as high stability in sulfur-containing syngas. CO conversion and DME selectivity were 66.5 and 64.0%, respectively, after a 20 h stream was applied at a sulfur-containing syngas, with a pressure of 3 MPa, temperature of 300 degrees C and space velocity of 1600 L kg(-1) h(-1).