Preparation Of Overgrowth-type MCM-41/H? Composite For Shape-selective Alkylation Of Phenol With Isopropanol

Although zeolites are shape selective, non-selective reactions may take place on the external surface of the zeolites. Selective attenuation of the external acid sites will reduce the formation of these by-products. However, the high selectivity may lead to the decrease of activity in many cases.To solve the problem, an overgrowth-type MCM-41/H? composite was synthesized by a conventional hydrothermal method and characterized by XRD, N2 adsorption-desorption, TEM, Py-IR and NH3-TPD. The characterization results indicated that MCM-41/H? composite were synthesized, presenting the existence of micro-phase zeolite Beta and meso-phase MCM-41. H? was covered by a MCM-41 layer, and the MCM-41 pore channels were found to be oriented outward from the inner HP core, which might be the reason why the diffusion of the molecules were not influenced while the non-selectivity sites of outer surface were suppressed.The effect of the molar ratio of cetyltrimethylammonium bromide (CTAB) or cetyltrimethylammonium chloride (CTAC) to silica, pH, synthesis temperature and time in the synthesis of composite were investigated. The results showed that the synthesis of MCM-41/H? composite was greatly influenced by the above factors. The optimized synthesis conditions of MCM-41/H? composite using CTAB as the template were as follows:the molar ratio of CTAB to silica 0.23, pH=11, synthesis temperature 120? and synthesis time 48 h. The optimized synthesis conditions of MCM-41/Hp using CTAC as the template were as follows:the molar ratio of CTAC to silica 0.26, pH=11,synthesis temperature 120? and synthesis time 48 h.The alkylation of phenol with isopropanol was investigated over MCM-41/H? composite, H?, MCM-41. The results showed that both the activity and the para selectivity of MCM-41 were very low. The para selectivity of MCM-41/H? was almost 10% higher than that of H?, while the loss of activity was negligible. This could be attributed to the structure of the MCM-41/H? composite. The external acid sites of H? were covered by a weakly acidic MCM-41 layer, but the mesoporous structure of this layer did not significantly hinder the diffusion of the molecules involved in the alkylation reaction.