Methylation of toluene with methanol to p-xylene over conventional HZSM-5 zeolites is accompanied by various unwanted reactions. Narrowing of pores and lowering of acidity of HZSM-5 zeolites to maximize p-xylene have resulted into trade-off between p-xylene selectivity and toluene conversion. ZSM-48 zeolites, owing to narrower pores and lower acidity than ZSM-5, can be useful for direct utilization for toluene methylation. Further, such zeolites with reduced crystal sizes can shorten the pore retention time for small and highly reactive methanol and eliminate diffusion limitations to toluene and p-xylene molecules respectively to avoid methanol overuse in side reactions and to improve catalytic activity for toluene methylation. Envisaging above advantages, objective of the present work is to synthesize nano size ZSM-48 zeolite and demonstrate combined role of its narrow pore, less acidity and small crystals in maximization of p-xylene in toluene methylation reaction. Morphology and crystal information for prepared ZSM-48 are obtained from Field Emission Scanning Electron Microscopy and High Resolution Transmission Electron Microscopy. Results revealed 44% p-xylene selectivity and 26% toluene conversion at 400 °C, improved methanol utilization and remarkable catalyst stability with no sign of drop in catalyst activity for 120 h time on stream study.

在传统的 HZSM-5 沸石上用甲醇将甲苯甲基化为对二甲苯会伴随各种不需要的反应。缩小孔隙和降低 HZSM-5 沸石的酸度以最大化对二甲苯导致对二甲苯选择性之间的权衡和甲苯转化。ZSM-48 沸石由于比 ZSM-5 孔隙更窄且酸度更低，可用于甲苯甲基化的直接利用。此外，这种晶体尺寸减小的沸石可以缩短小分子和高反应性甲醇的孔保留时间，并分别消除对甲苯和对二甲苯分子的扩散限制，以避免甲醇在副反应中过度使用并提高甲苯甲基化的催化活性。考虑到上述优点，本工作的目标是合成纳米尺寸的 ZSM-48 沸石，并证明其孔隙窄、酸度低和晶体小在甲苯甲基化反应中对二甲苯最大化的综合作用。制备的 ZSM-48 的形态和晶体信息是从场发射扫描电子显微镜获得的和高分辨率透射电子显微镜。结果表明，在 400 °C 下，对二甲苯选择性为 44%，甲苯转化率为 26%，提高了甲醇利用率和显着的催化剂稳定性，在 120 小时的运行研究中催化剂活性没有下降的迹象。