Hierarchical composite catalysts of MCM-41 on zeolite Beta for conversion of heavy reformate to xylenes

Hierarchical composites of MCM-41 on zeolite Beta were synthesized by in-situ hydrothermal technique, characterized and their catalytic performance for converting heavy reformate into valuable xylenes was evaluated. Systematic optimization of the hierarchical pore generation was carried out by varying the strength of the alkaline solution (0.10−0.45 M NaOH) during disintegration of zeolite Beta. The nanocomposites obtained were extruded with alumina binder and impregnated with 4.0 wt% Mo. The characterization results indicate the transition of mesophase occurs from distinct disordered phase to ordered/disordered and then to ordered mesophase with increasing alkaline concentration. The xylene yield over the hierarchical composite zeolite was 1.4 times more than the parent zeolite Beta. Incorporation of a well-dispersed mild hydrogenation function (4 wt.% Mo) was advantageous in improving the xylene yield and selectivity. The formulation prepared with moderately alkaline (0.2 M NaOH) solution exhibited optimum bimodal pore structure and improved dealkylation and transalkylation conversion resulting in a xylene yield of 33.0 wt.% and 1.7 times enhancement in xylene selectivity over parent zeolite Beta. A 30 h stability test showed steady performance and xylene yields. Hence, a potential application of hierarchical zeolite Beta and MCM-41 composite catalysts for the conversion of heavy aromatics to produce xylenes has been successfully demonstrated.