Aiming at a better understanding of the unusual low-temperature CO oxidation reaction behavior on Au/Mg(OH)₂ catalysts, we investigated this reaction mainly by combined kinetic and in situ IR spectroscopy measurements over a wide range of temperatures, from −90 °C to 200 °C. Catalysts with a very narrow Au particle size distribution were prepared by colloidal deposition. Kinetic measurements, performed under differential, dry reaction conditions at different constant temperatures, enabled the separation of thermal and deactivation effects. They revealed that the distinct reaction behavior, with an exceptionally high activity at temperatures below 0 °C and decreasing CO oxidation rates in the range between −50 °C and 30 °C, equivalent to a negative apparent activation energy, does not result from either deactivation effects or H₂O trace impurities, but is an intrinsic feature of the reaction. An unusual temperature dependence was also observed for the tendency for deactivation, with a pronounced maximum at −20 °C, which mainly results from an accumulation of surface carbonate species blocking active reaction sites or access of adsorbed reactants to them. Similar measurements on Au/TiO₂ catalysts revealed that the high activity of Au/Mg(OH)₂ in the low-temperature range compared to Au/TiO₂ is first of all due to the weaker interactions of Mg(OH)₂ with CO₂ compared to TiO₂. This leads to an increasing tendency of CO₂ product molecules to adsorb on the latter catalyst at reaction temperatures below 0 °C and hence to rapid ‘self-poisoning’ with CO₂ desorption as the rate-limiting step. For Au/Mg(OH)₂, CO₂ desorption is much faster, allowing much higher rates in the continuous CO oxidation. Based on temporal analysis of products (TAP) reactor measurements, the decay of the reaction rates in the range −50 °C to +50 °C is tentatively attributed to a decreasing steady-state coverage of weakly bound molecularly adsorbed O₂ with increasing temperature, while stable adsorbed active surface oxygen is negligible over the entire range of reaction temperatures investigated. The implications of these and earlier findings for the mechanistic understanding of the low-temperature CO oxidation on Au/Mg(OH)₂ and support effects therein are discussed.

中文翻译：

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低温CO氧化中的高活性和负表观活化能–存在于Au / Mg（OH）_2上，不存在于Au / TiO _2上

为了更好地了解Au / Mg（OH）₂催化剂上异常低温CO氧化反应的行为，我们主要通过结合动力学和原位研究了该反应红外光谱法可在-90°C至200°C的较宽温度范围内进行测量。通过胶体沉积制备具有非常窄的Au粒度分布的催化剂。在不同的恒定温度，不同的干燥反应条件下进行的动力学测量能够分离热效应和失活效应。他们发现，独特的反应行为在低于0°C的温度下具有极高的活性，并且在-50°C和30°C之间的范围内降低了CO氧化速率，这与负表观活化能均不相同，失活效应或H ₂O微量杂质，但是是反应的固有特征。还观察到了失活趋势的不寻常的温度依赖性，在-20°C时有明显的最大值，这主要是由于表面碳酸盐物质的积累阻止了活性反应位点或吸附的反应物接近它们而导致的。在Au / TiO ₂催化剂上进行的相似测量表明，与Au / TiO ₂相比，Au / Mg（OH）₂在低温范围内的高活性首先是由于Mg（OH）₂与CO的相互作用较弱。₂与TiO ₂相比。这导致CO ₂增加的趋势产物分子在低于0°C的反应温度下吸附到后一种催化剂上，因此通过限速步骤将CO ₂解吸快速“自中毒” 。对于Au / Mg（OH）₂，CO _2的解吸快得多，从而允许连续CO氧化的速率更高。根据产品（TAP）反应器测量的时间分析，在-50°C到+50°C范围内，反应速率的下降暂时归因于弱结合的分子吸附O _2的稳态覆盖率降低随着温度的升高，在整个研究温度范围内，稳定的活性表面氧的吸附量可忽略不计。讨论了这些和更早的发现对于在Au / Mg（OH）₂上进行低温CO氧化的机理及其支持作用的意义。