氧化镍改性的ZSM-5催化剂对甲苯和甲醇择形甲基化反应稳定性的影响

在常压下，以N₂为载气，采用固定床反应器考察了NiO改性的ZSM-5催化剂催化甲苯和甲醇择形烷基化反应的性能。采用Ar物理吸附、XRD、XRF、TEM、XPS、H₂-TPR、NH₃-TPD、Py-IR、UV-Vis、UV-Raman、TG、GC-MS等手段表征所制备的催化剂。结果表明，在ZSM-5催化剂上负载质量分数为3%或5%的Ni，催化剂的稳定性明显得到提高。在催化甲苯甲基化反应后，NiO改性ZSM-5催化剂上出现了金属Ni，这可能是由于在积炭过程中，伴随着氢转移过程或者是水消炭反应过程而产生的H2将NiO还原为金属Ni；而且，催化剂的积炭量明显降低，同时作为积炭前驱体的稠环芳烃的生成量也明显减少，推测可能是由于金属Ni的存在，抑制了烷基苯脱氢生成稠环芳烃积炭前驱体的反应，因而提高了催化剂的稳定性。

Effect of NiO Modification on Stability of Nano-sized ZSM-5 Catalyst for the Para-Selective Methylation of Toluene with Methanol

Shape-selective methylation of toluene with methanol was carried out in a fixed-bed tubular reactor with a continuous down-flow over Ni doped ZSM-5 catalysts, with N₂ as carrier gas under atmospheric pressure. All the catalysts were characterized by Ar-physisorption, XRD, XRF, TEM, XPS, H₂-TPR, NH₃-TPD, Py-IR, UV-Vis, UV-Raman, TG and GC-MS. The results showed that the catalytic stability of the ZSM-5 catalyst was significantly enhanced with Ni loading at 3% and 5%. The metal Ni is present on the spent catalysts, due to the hydrogen from hydrogen transfer reaction or the reaction between water and coke, which could reduce NiO to metal Ni within the coking process. The coke amounts were decreased by introducing Ni species, so were the highly condensed aromatics as coke precursors. The presence of metal Ni led to significant suppression of dehydrogenation and condensation, thus inhibition of the coking process, resulting in the improvement of catalyst stability.