Abstract

The precursors of Ni/Al₂O₃ catalysts with different metal contents (2–10 wt % Ni) and calcination temperatures were obtained by wet impregnation. Their composition and physicochemical properties were determined by low-temperature nitrogen adsorption, atomic absorption spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), and temperature-programmed reduction (TPR) with hydrogen. The formation of free and chemically bound forms of nickel was studied by TPR-H₂. Calcination above 400°C leads to complete binding of nickel with Al₂O₃, forming nickel–aluminum spinel. According to TPR-H₂, free NiO appears in the samples calcinated at 550°C only at 10% Ni. The stability of the reduced catalysts to oxidation in air and the effect of the temperature of treatment with hydrogen on the reduction of the nickel forms bonded with the support were determined. The XPS and TPR studies showed that the oxidation of reduced nickel in air led to a transition from Ni²⁺ forms tightly bound with support to weakly bound forms that are more easily reduced. The catalytic action in hydrodechlorination of chlorobenzene (CB HDC) of the samples that differed in the ratio of weakly and tightly bound Ni forms was considered. The spinel forms that are nearly inactive in chlorobenzene hydrodechlorination can be reduced with hydrogen to form more active Ni⁰ sites under the reaction conditions. The active sites obtained by the reduction of Ni²⁺ forms weakly bound to the support are stable under chlorobenzene hydrodechlorination conditions.

中文翻译：

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煅烧温度对Ni / Al 2 O 3加氢脱氯反应效率的影响

摘要

通过湿法浸渍获得了具有不同金属含量（2-10 wt％Ni）和煅烧温度的Ni / Al ₂ O ₃催化剂的前体。通过低温氮吸附，原子吸收光谱，扫描电子显微镜，高分辨率透射电子显微镜，X射线光电子能谱（XPS）和氢程序升温还原（TPR）来确定它们的组成和理化性质。通过TPR-H ₂研究了游离和化学键合形式的镍的形成。在400°C以上煅烧会导致镍与Al ₂ O ₃完全结合，形成镍铝尖晶石。根据TPR-H ₂，仅在10％Ni下在550°C煅烧的样品中出现游离NiO。确定了还原的催化剂在空气中氧化的稳定性以及氢处理温度对与载体结合的镍形式的还原的影响。XPS和TPR研究表明，空气中还原的镍的氧化导致从与载体紧密结合的Ni ²⁺形式转变为更易于还原的弱结合形式。考虑了弱和紧密结合的镍形式的比例不同的样品在氯苯加氢脱氯中的催化作用。可用氢还原在氯苯加氢脱氯中几乎不活泼的尖晶石形式，以形成更具活性的Ni ⁰反应条件下的位点。通过还原弱结合到载体上的Ni ²⁺形式获得的活性位点在氯苯加氢脱氯条件下是稳定的。