The transformation of Lewis acid to new Brønsted acid upon hydrogen exposure of tungsten oxide supported on mesoporous spherical silica nanoparticles (SSP) catalysts has been investigated by in situ diffuse reflection infrared Fourier transform spectroscopy (DRIFTS) with adsorbed NH₃. The principal goal of this work is to explore the influence of W species on the support and the activating processes involved in the formation of catalytically active sites for Lewis acid transformation. The samples were prepared by two preparation methods including incipient wetness impregnation and incorporation of W species to SSP support with the sol–gel method. Then, they were activated by N₂ pretreatment compared with H₂ before investigation. From the results of in situ DRIFTS experiments, the Lewis acid sites were changed to the Brønsted acid sites upon hydrogen exposure over activated catalysts. The abundance of tungstate W⁵⁺ species is found to facilitate the change of this acidity. In addition, the performance of Lewis acid transformation was correlated with tungstate W⁵⁺ active species, which could be more generated by activating process of H₂ and N₂ pretreatments. The impregnated W/SSP needs H₂ pretreatment to activate active site formation, while the incorporated W-SSP can be activated in both of H₂ and N₂ pretreatments because the latter prefers the formation of tungstate W⁵⁺ species in catalyst, instead of W dispersed on SSP surface to form W surface structure characteristic of the W⁶⁺ species.

中文翻译：

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球形二氧化硅催化剂上WO _x上的活性位点形成，可将路易斯酸转化为布朗斯台德酸活性

通过原位扩散反射红外傅里叶变换光谱法（DRIFTS）研究了吸附有NH _3的氧化钨在介孔球形二氧化硅纳米粒子（SSP）催化剂上负载的氢暴露后，路易斯酸向新布朗斯台德酸的转化。这项工作的主要目的是探讨W物种对支持物和影响路易斯酸转化的催化活性位点形成过程中的活化过程的影响。通过两种制备方法制备样品，包括初期湿润浸渍和通过溶胶-凝胶法将W物种掺入SSP载体中。然后，与H ₂相比，通过N ₂预处理将它们激活在调查之前。根据原位DRIFTS实验的结果，在活化催化剂上暴露于氢后，路易斯酸位点变为布朗斯台德酸位点。发现丰富的钨酸盐W ⁵⁺物种有助于改变这种酸度。此外，路易斯酸转化的性能与钨酸W ⁵⁺活性物质有关，而钨酸W ⁵⁺活性物质可能是通过H ₂和N ₂预处理的活化过程产生的。浸渍的W / SSP需要进行H ₂预处理以激活活性位点形成，而掺入的W-SSP则可以同时在H ₂和N _2中被激活。进行预处理，因为后者更喜欢在催化剂中形成钨酸盐W ⁵⁺物种，而不是将W分散在SSP表面上以形成W ⁶⁺物种的W表面结构特征。