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Nonoxidative dehydrogenation and aromatization of methane over W/HZSM-5-based catalysts

机译：W / HZSM-5基催化剂上甲烷的非氧化脱氢和芳构化

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Highly active and heat-resisting W/HZSM-5-based catalysts for nonoxidative dehydro-aromatization of methane (DHAM) have been developed and studied. It was found from the experiments that the W-H2SO4/HZSM-5 catalyst prepared from a H2SO4-acidified solution of ammonium tungstate (with a pH value at 2-3) displayed rather high DHAM activity at 973-1023 K, whereas the W/HZSM-5 catalyst prepared from an alkaline or neutral solution of (NH4)(2)WO4 showed very little DHAM activity at the same temperatures. Laser Raman spectra provided evidence for existence of(WO6)(n-) groups constructing polytungstate ions in the acidified solution of ammonium tungstate. The H-2-TPR results showed that the reduction of precursor of the 3% W-H2SO4/HZSM-5 catalyst may occur at temperatures below 900 K, producing W species with mixed valence states, W5+ and W4+, whereas the reduction of the 3% W/HZSM-5 occurred mainly at temperatures above 1023 K, producing only one type of dominant W species, W5+. The results seem to imply that the observed high DHAM activity on the W-H2SO4/HZSM-5 catalyst was closely correlated with (WO6)(n-) groups with octahedral coordination as the precursor of catalytically active species. Incorporation of Zn (or La) into the W-H2SO4/HZSM-5 catalyst has been found to pronouncedly improve the activity and stability of the catalyst for DHAM reaction. Over a 2.5% W-1.5% Zn-H2SO4/HZSM-5 catalyst and under reaction conditions of 1123 K, 0.1 MPa, and GHSV = 1500 ml/(hg-cat.), methane conversion (X-CH4) reached 23% with the selectivity to benzene at similar to 96% and an amount of coke for 3 h of operation at 0.02% of the catalyst weight used.
机译：已经开发和研究了用于甲烷的非氧化脱氢芳构化的高活性和耐热W / HZSM-5基催化剂。从实验中发现，由钨酸铵的H2SO4酸化溶液（pH值为2-3）制备的W-H2SO4 / HZSM-5催化剂在973-1023 K时显示出相当高的DHAM活性，而W由（NH4）（2）WO4的碱性或中性溶液制备的/ HZSM-5催化剂在相同温度下几乎没有DHAM活性。激光拉曼光谱提供了在钨酸铵酸化溶液中存在构成聚钨酸根离子的（WO6）（n-）基团的证据。 H-2-TPR结果表明，3％W-H2SO4 / HZSM-5催化剂的前体还原可能在900 K以下的温度下发生，产生具有混合价态W5 +和W4 +的W物种，而3％W / HZSM-5主要发生在1023 K以上的温度下，仅产生一种主要的W物种W5 +。结果似乎暗示在W-H2SO4 / HZSM-5催化剂上观察到的高DHAM活性与具有八面体配位的（WO6）（n-）基团密切相关，后者是催化活性物质的前体。已发现将Zn（或La）掺入W-H 2 SO 4 / HZSM-5催化剂中可显着改善DHAM反应的催化剂的活性和稳定性。在2.5％W-1.5％Zn-H2SO4 / HZSM-5催化剂上，在1123 K，0.1 MPa和GHSV = 1500 ml /（hg-cat。）的反应条件下，甲烷转化率（X-CH4）达到23％苯的选择性接近96％，操作3小时的焦炭量为所用催化剂重量的0.02％。

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