Oxidative cleavage of carbon–carbon double bonds (C═C) in alkenes and fatty acids produces aldehydes and acids valued as chemical intermediates. Solid tungsten oxide catalysts are low cost, nontoxic, and selective for the oxidative cleavage of C═C bonds with hydrogen peroxide (H₂O₂) and are, therefore, a promising option for continuous processes. Despite the relevance of these materials, the elementary steps involved and their sensitivity to the form of W sites present on surfaces have not been described. Here, we combine in situ spectroscopy and rate measurements to identify significant steps in the reaction and the reactive species present on the catalysts and examine differences between the kinetics of this reaction on isolated W atoms grafted to alumina and on those exposed on crystalline WO₃ nanoparticles. Raman spectroscopy shows that W–peroxo complexes (W–(η²-O₂)) formed from H₂O₂ react with alkenes in a kinetically relevant step to produce epoxides, which undergo hydrolysis at protic surface sites. Subsequently, the CH₃CN solvent deprotonates diols to form alpha-hydroxy ketones that react to form aldehydes and water following nucleophilic attack of H₂O₂. Turnover rates for oxidative cleavage, determined by in situ site titrations, on WO_x–Al₂O₃ are 75% greater than those on WO₃ at standard conditions. These differences reflect the activation enthalpies (ΔH^‡) for the oxidative cleavage of 4-octene that are much lower than those for the isolated WO_x sites (36 ± 3 and 60 ± 6 kJ·mol^–1 for WO_x–Al₂O₃ and WO₃, respectively) and correlate strongly with the difference between the enthalpies of adsorption for epoxyoctane (ΔH_ads,epox), which resembles the transition state for epoxidation. The WO_x–Al₂O₃ catalysts mediate oxidative cleavage of oleic acid with H₂O₂ following a mechanism comparable to that for the oxidative cleavage of 4-octene. The WO₃ materials, however, form only the epoxide and do not cleave the C–C bond or produce aldehydes and acids. These differences reflect the distinct site requirements for these reaction pathways and indicate that acid sites required for diol formation are strongly inhibited by oleic acids and epoxides on WO₃ whereas the Al₂O₃ support provides sites competent for this reaction and increase the yield of the oxidative cleavage products.

中文翻译：

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氧化钨催化剂上H ₂ O ₂对4-辛烯和油酸与H ₂ O ₂的氧化裂解的反应物种和反应途径

烯烃和脂肪酸中碳-碳双键（C═C）的氧化裂解会产生醛和酸，它们被视作化学中间体。固态氧化钨催化剂价格低廉，无毒且对用过氧化氢（H ₂ O ₂），因此是连续过程的理想选择。尽管这些材料相关，但尚未描述所涉及的基本步骤及其对表面上W位置形式的敏感性。在这里，我们结合原位光谱和速率测量来确定反应中的重要步骤和催化剂上存在的反应性物种，并检查该反应动力学对接枝到氧化铝上的孤立W原子和在结晶WO ₃纳米颗粒上暴露的那些动力学之间的差异。。拉曼光谱显示，W-过氧复合物（W-（η ² -O ₂））选自H形成₂ ö ₂在动力学上相关的步骤中与烯烃反应生成环氧化物，该环氧化物在质子表面位点发生水解。随后，CH ₃ CN溶剂使二醇去质子化以形成α-羟基酮，在H ₂ O _2发生亲核攻击后，后者反应形成醛和水。在标准条件下，WO _x -Al ₂ O ₃上通过原位滴定法测定的氧化裂解的转换速率比WO _3的转换速率高75％。这些差异反映了4-辛烯的氧化裂解的活化焓（ΔH ^‡）远低于分离的WO _x的活化焓（ΔH ^‡）。位点（36±3和60±6千焦·摩尔^-1为WO _X -Al ₂ ö ₃和WO ₃，分别地），并用吸附的对环氧辛烷焓（之间的差相关成分强烈ΔH_{广告，磐英}），它类似于环氧化的过渡态。WO _x -Al ₂ O ₃催化剂以与4-辛烯氧化裂解相当的机理介导油酸与H ₂ O ₂的氧化裂解。WO ₃但是，这些材料仅形成环氧化物，不会裂解C–C键或产生醛和酸。这些差异反映了这些反应途径的不同位点要求，并表明二醇形成所需的酸位点受到WO ₃上的油酸和环氧化物的强烈抑制，而Al ₂ O ₃载体则提供了适合该反应的位点并增加了反应的收率。氧化裂解产物。