Influence of different metal-modified Beta zeolites on the liquid-phase isomerisation of xylene and reaction mechanisms

PX is a very important chemical raw material. There are few studies on the liquid-phase isomerisation of xylene. Here, a series of Beta catalysts with different metal modifications were prepared and tested for many characterisations. The reaction performance of the catalysts was evaluated in the liquid-phase MX isomerisation reaction. The results show that the loading of La, Ce, Mo,Fe and Mg metals decreases the specific surface area and acid content of Beta zeolite. Among them, Mo has a strong interaction with the skeleton Al atoms in Beta. The side reactions of MX isomerisation were inhibited by metal loading, and the selectivity of PX and OX was improved. The effect of Mo content on the liquid-phase isomerisation of MX was further investigated. The selectivity of PX can be improved by appropriate Mo content. This is related to the reaction mechanism of the liquid-phase isomerisation of MX at mainly low temperatures. The acidic site density of B and L acids on the catalyst surface was successfully modulated by Mo loading. At 260 degrees C, the conversion of MX over Mo/Beta catalyst was about 33 % and the PX yield was 12.83 %. In addition, based on the results of liquid-phase isomerisation of MX, OX and PX, the transformation relationship between the three isomers was investigated.