Alkali treatment is widely used on aluminosilicate zeolites with high Si/Al ratios in order to fabricate mesopores in the framework. However, for zeolites with low Si/Al ratios, the effect of alkali treatment on the pore and framework structure needed further study. In this work, Y zeolite is treated with NaOH solutions of different concentrations and is used as the support for Cu-based catalysts for oxidative carbonylation of methanol to dimethyl carbonate. The physicochemical properties of the supports and corresponding catalysts are characterized by N2 adsorption–desorption, X-ray diffraction, X-ray fluorescence, transmission electron microscopy, inductively coupled plasma mass spectrometry, X-ray photoelectron spectroscopy, and H2-temperature-programmed reduction analyses. The results show that no obvious mesopores are formed under alkali treatment, even at high NaOH concentration. However, amorphous species present in the micropores of Y zeolite are removed, which increases the micropore surface area as well as the crystallinity. Simultaneously, the cage structure is partially destroyed, which also leads to a slight increase of the pore volume and surface area. The altered micropore structure eventually increases the content and accessibility of the exchanged Cu species, which is beneficial to the catalytic activity. When the concentration of NaOH is 0.6 M, the space time yield of dimethyl carbonate for the corresponding catalyst was 151.4 mg g−1 h−1 which is 3.3-fold higher than that of the untreated-Y-zeolite-supported Cu catalyst. However, further increasing the alkali treatment strength can seriously destroy the basic aluminosilicate structure of the Y zeolite and decrease its intrinsic ion-exchange capacity. This results in the formation of agglomerated CuO on the catalyst surface, which was not conducive to catalytic activity.

中文翻译：

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NaY沸石在碱处理过程中孔隙和骨架结构的演变及其对CuY催化剂甲醇氧化羰基化的影响

碱处理广泛用于具有高 Si/Al 比的铝硅酸盐沸石，以在骨架中制造中孔。然而，对于低硅铝比的沸石，碱处理对孔结构和骨架结构的影响需要进一步研究。在这项工作中，Y 沸石用不同浓度的 NaOH 溶液处理，并用作铜基催化剂的载体，用于甲醇氧化羰基化生成碳酸二甲酯。载体和相应催化剂的理化性质通过 N2 吸附-解吸、X 射线衍射、X 射线荧光、透射电子显微镜、电感耦合等离子体质谱、X 射线光电子能谱和 H2 程序升温还原表征分析。结果表明，即使在高NaOH浓度下，碱处理也没有形成明显的介孔。然而，Y沸石微孔中存在的无定形物质被去除，这增加了微孔表面积以及结晶度。同时，笼状结构被部分破坏，这也导致孔体积和表面积略有增加。改变的微孔结构最终增加了交换的 Cu 物种的含量和可及性，这有利于催化活性。当NaOH浓度为0.6 M时，相应催化剂的碳酸二甲酯时空产率为151.4 mg g-1 h-1，是未处理的Y-沸石负载Cu催化剂的3.3倍。然而，进一步提高碱处理强度会严重破坏Y型沸石的基本硅铝酸盐结构，降低其固有的离子交换能力。这导致在催化剂表面形成团聚的CuO，不利于催化活性。