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首页> 外文期刊>Catalysis science & technology >High activity and negative apparent activation energy in low-temperature CO oxidation -present on Au/Mg(OH)(2), absent on Au/TiO2
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High activity and negative apparent activation energy in low-temperature CO oxidation -present on Au/Mg(OH)(2), absent on Au/TiO2

机译：高活动和负明显激活能源在低温氧化存在非盟/毫克(OH)(2),在非盟/二氧化钛缺席

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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 degrees C to 200 degrees 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 degrees C and decreasing CO oxidation rates in the range between -50 degrees C and 30 degrees 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 degrees 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 degrees 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 degrees C to +50 degrees C is tentatively attributed to a decreasing steady-state coverage of weakly bound molecularly adsorbed O-2 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.
机译：旨在更好地理解的不同寻常低温氧化反应行为非盟/毫克(OH)(2)催化剂,我们调查主要是通过结合动力学和原位反应在广泛的红外光谱测量温度,从-90度到200度与一个非常狭窄的盟催化剂粒度分布是由胶体沉积。差,干燥的反应条件不同的恒定温度,使热分离和失活的影响。他们显示不同的反应行为,异常高的活动温度低于0摄氏度,减少有限公司氧化率之间-50度摄氏30度,相当于一个负面的表观活化能,没有结果失活效应或水痕迹杂质,但是是一种固有的特性的反应。还观察到失活的趋势,与明显的最大值-20摄氏度主要从表面的积累结果碳酸盐物种屏蔽网站积极反应或访问的吸附反应物。测量非盟/二氧化钛催化剂显示非盟的高活动/毫克(OH) (2)低温范围相比,非盟/二氧化钛首先由于较弱的相互作用毫克(OH)(2)与二氧化碳相比,二氧化钛。二氧化碳的增加趋势的产品分子吸附在后者的催化剂反应温度低于0摄氏度,因此快速自我毒害与二氧化碳解吸病原反应步骤。解吸速度更快,使高得多利率在连续CO氧化。时序分析的产品(TAP)反应堆测量,反应速率的衰减-50摄氏度到+ 50摄氏度初步认为减少稳态弱束缚分子的报道吸附-随着温度、时间稳定的吸附活性表面氧微不足道的整个范围的反应温度影响。这些机械和早期的发现对低温CO氧化的理解非盟/毫克(OH)(2)和支持其中的影响进行了讨论。

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