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首页> 外文期刊>Catalysis science & technology >Methanol-to-olefins process over zeolite catalysts with DDR topology: effect of composition and structural defects on catalytic performance
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Methanol-to-olefins process over zeolite catalysts with DDR topology: effect of composition and structural defects on catalytic performance

机译：Methanol-to-olefins过程沸石催化剂DDR拓扑结构:组成和效果对催化性能的结构性缺陷

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摘要

A systematic study of the effect of physicochemical properties affecting catalyst deactivation, overall olefin selectivity and ethylene/propylene ratio during the methanol-to-olefins (MTO) reaction is presented for two zeolites with the DDR topology, namely Sigma-1 and ZSM-58. Both catalysts show high selectivity towards light olefins and completely suppress the formation of hydrocarbons bigger than C4, with selectivity to ethane not exceeding 1% and some traces of propane. By applying seeded growth approach, a series of Sigma-1 zeolites with tunable crystal size and acidity was synthesized. For this series the highest methanol throughput at 450 degrees C before deactivation was found for crystals 0.5 mu m in size with an acidity corresponding to 0.5 Al atoms per zeolite cage, and a selectivity to ethylene and propylene reaching 90%. Comparison between ZSM-58 and Sigma-1 catalysts with similar morphologies and acidity under the same reaction conditions revealed a three times higher throughput of methanol in case of ZSM-58. The analysis of functional surface groups, assessed through FT-IR, revealed the presence of silanol defects in Sigma-1 responsible for faster catalyst deactivation. These silanol defects can be selectively removed (confirmed by FT-IR) from the zeolite framework by applying a mild treatment in presence of NaOH/CTAB, leading to an improved catalyst lifetime. Co-feeding experiments with short olefins and water show low reactivity of primary MTO products, which only react at the surface of the catalyst particles. These results demonstrate that migration of the reaction zone in case of DDR catalysts hardly affects catalyst stability, product composition and nature of deactivating species. The nature of these species depends mostly on reaction temperature: at low temperatures deactivation occurs mainly due to the formation of inert adamantane species, while at high temperatures poly-condensed aromatic hydrocarbons play the major role in deactivation.
机译：一个系统的学习的影响物理化学性质影响催化剂失活,总体烯烃选择性乙烯/丙烯在比例methanol-to-olefins (MTO)反应两种沸石的DDR拓扑结构,即sigma 1和ZSM-58。对轻烯烃选择性和完全碳氢化合物的形成抑制大比C4,选择性乙烷不超过1%和丙烷的一些痕迹。增长方式,一系列的sigma 1沸石与可调水晶大小和酸度合成。吞吐量在450摄氏度失活发现水晶0.5μm的尺寸有吗对应于0.5铝原子/沸石的酸性笼,乙烯和丙烯的选择性达到了90%。与类似的形态和sigma 1催化剂在相同的反应条件下酸性显示更高的吞吐量的三倍甲醇ZSM-58。功能表面组织,通过评估傅立叶变换红外光谱,发现硅醇的存在缺陷在sigma 1负责更快的催化剂失活。有选择地删除(红外光谱证实了)沸石框架通过应用一个温和的治疗氢氧化钠/ CTAB,导致一种改进催化剂寿命。短的烯烃和水显示低反应性的主要MTO产品,只有在反应催化剂表面的粒子。证明迁移反应的区域DDR催化剂几乎不影响催化剂稳定性、产品的组成和性质物种才会安静下来。主要取决于反应温度:在低高温失活主要是由于发生惰性金刚烷物种的形成,在高温下poly-condensed芳香碳氢化合物在失活中发挥主要作用。

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