A transient kinetic analysis of the evolution of a reducible metal oxide towards catalyzing nonoxidative alkanol dehydrogenation
A transient kinetic analysis of the evolution of a reducible metal oxide towards catalyzing nonoxidative alkanol dehydrogenation
复制标题
DOI：
10.1016/j.jcat.2020.08.023
复制
发表时间：
2020-08
影响因子：
7.3
通讯作者：
S. Afrin;Praveen Bollini
中科院分区：
文献类型：
--
作者：
S. Afrin;Praveen Bollini
对四组好氧/厌氧乙醇转化瞬态的定量分析表明，天然高表面积氧化铈表面的演变，影响了乙醇氧化转化的一半还原，在完全表面还原后，只催化非氧化乙醇脱氢。498 K下的好氧-厌氧开关导致新的稳态脱氢速率，而不是催化乙醛生成的终止。在厌氧实验中，同时终止氧失衡（反映氧化铈还原）和诱导期（反映活性位点的产生）表明，乙醇脱氢周转源于表面还原。当使用乙醛和co2生成速率时，从氧不平衡分析中获得的令人难以置信的高空位密度，与使用水和co2生成速率时获得的空位密度不同，表明至少部分乙醛是在好氧-厌氧开关和厌氧诱导期间形成的。归一化水摩尔流量，用于衡量催化和化学计量途径对乙醛形成的相对贡献，证明了在逐步表面还原过程中从化学计量乙醇氧化到催化乙醇脱氢的转变。高温氢气预处理可用于控制乙醇脱氢对乙醛整体形成的初始贡献，以及乙醇而不是氢分子产生的部分表面还原。另一方面，像苯酚这样的无氢滴定剂可以用来滴定催化烷基醇脱氢的位点，而不会改变首先负责位点创建的化学计量学路线的流行。本文使用的瞬态实验的结合，清晰地捕捉到了高表面积氧化铈对乙醇的催化功能的演变，这种催化功能源于其在天然的，完全氧化的表面上的化学计量转换。同样重要的是，研究结果还指出了一条在可还原金属氧化物上无水合成烷烃的途径。
Quantitative analyses of four sets of aerobic/anaerobic ethanol conversion transients point to the evolution of a native high-surface-area cerium oxide surface that effects the reduction half of the ethanol oxidation turnover to catalyzing, exclusively, nonoxidative ethanol dehydrogenation upon complete surface reduction. Aerobic–anaerobic switches at 498 K lead to new steady state dehydrogenation rates, rather than termination of catalytic acetaldehyde formation. Concurrent termination of oxygen imbalances (reflecting ceria reduction) and induction periods (reflecting active site creation) in anaerobic experiments point to ethanol dehydrogenation turnovers owing their provenance to surface reduction. Implausibly high vacancy densities obtained from analysis of oxygen imbalances when using acetaldehyde and CO2formation rates, unlike those obtained when using water and CO2formation rates, point to the catalytic origin of at least part of the acetaldehyde formed during both aerobic–anaerobic switches and anaerobic induction periods. Normalized water molar flow rates, used as a measure of the relative contributions of catalytic and stoichiometric routes to acetaldehyde formation, evince a transition from stoichiometric ethanol oxidation to catalytic ethanol dehydrogenation upon progressive surface reduction. High-temperature hydrogen pretreatments can be used to manipulate both the initial contribution of ethanol dehydrogenation to overall acetaldehyde formation as well as the fractional surface reduction that ethanol, rather than molecular hydrogen, effectuates. Alpha hydrogen-free titrants such as phenol, on the other hand, can be used to titrate sites contributing to catalytic alkanol dehydrogenation without altering the prevalence of stoichiometric routes responsible for site creation in the first place. The combination of transient experiments used herein capture, with clarity, the evolution in catalytic function of high-surface-area cerium oxide toward ethanol upon progressive reduction that originates from its stoichiometric conversion over a native, fully oxidized surface. Not unimportantly, the results also point to an avenue for the water-free synthesis of alkanals over reducible metal oxides.