Preparation, Characterization and Shape-Selective Catalysis of Supported Heteropolyacid Salts K_(2.5)H_(0.5)PW_(12)O_(40), (NH4)H_(0.5)PW_(12)O_(40), and Ce_(0.83)H_(0.5)PW_(12)O_(40) on MCM-41 Mesoporous Silica

摘要

Supported heteropolyacid salts on MCM-41 as mesoporous materials with a strong acidity, K_(2.5)H_(0.5)PW_(12)O_(40)/ MCM-41, (NH4)_(2.5)H_(0.5)PW_(12)O_(40)/MCM-41, and Ce_(0.83)H_(0.5)PW_(12)O_(40)/MCM-41, were prepared by two-step impregnation and applied for shape-selective catalysis. The first impregnation of H3PW_(12)O_(40) accompanying the thermal treatment at 473 K and the second impregnation of cation salts accompanying the thermal treatment at 573 K are two key procedures for obtaining highly dispersed heteropolyacid salts on MCM-41. The Keggin structure of the heteropolyacid salts remains with a significant interaction between heteropolyanions and MCM-41 substrate, and MCM-41 texture is unchanged during loading of heteropolyacid salts. The acidities of the as-synthesized heteropolyacid salt/MCM-41s, with predominant Bronsted acidic sites, are much stronger than that of zeolite Y or Al-MCM-41, Close to those of Cs_(2.5)H_(0.5)PW_(12)O_(40)/MCM-41 and H3PW_(12)O_(40)/MCM-41. Compared to bulk heteropolyacid salts, zeolite Y and Al-MCM-41, the as-synthesized heteropolyacid salt/ MCM-41s show the shape-selectivity for the catalyzing alkylation reaction of benzene and 1-dodecene to monoalkyl-benzene with high reactivity. Moreover, K_(2.5)H_(0.5)PW_(12)O_(40)/MCM-41 and Ce_(0.83)H_(0.5)PW_(12)O_(40)/MCM-41 have a low deactivation rate for catalysis with a high hydrothermal stability, superior to Cs_(2.5)H_(0.5)PW_(12)O_(40)/ MCM-41 and H3PW_(12)O_(40)/MCM-41.