In many catalytic processes, metastable reaction intermediates are more valuable and desirable than final products. Here, we report Ni–Ni^δ+ clusters on ceria where the extent of reduction of nickel oxide/ceria in H₂ has been optimized. This catalyst shows high selectivity in reducing nitrobenzene to azoxybenzene, the latter usually being metastable. Due to strong electronic metal–support interactions between Ni and ceria, mixed Ni–Ni^δ+ clusters are formed on ceria even after reduction at 500 °C in hydrogen. The Ni–Ni^δ+ clusters are highly dispersed on ceria, as observed by high-angle annular dark-field scanning–transmission electron microscopy and energy-dispersive X-ray spectroscopy element mapping. This structural uniqueness is clearly reflected in the inhibition of azoxybenzene hydrogenation to aniline, and therefore the catalyst shows high azoxybenzene selectivity (92%). In comparison, the Ni metal catalyst mostly gives aniline and the NiO catalyst has low activity. This study shows how to steer catalytic reactions toward metastable intermediate products by tuning the extent of reduction of metal oxides deposited on reducible oxides.

在许多催化过程中，亚稳定的反应中间体比最终产品更有价值，更合乎要求。在这里，我们报告了氧化铈上的Ni– ^Niδ+团簇，其中H _2中氧化镍/氧化铈的还原程度得到了优化。该催化剂显示出将硝基苯还原成a氧基苯的高选择性，后者通常是亚稳的。由于镍和二氧化铈之间强烈的电子金属-载体相互作用，即使在氢气中于500°C还原后，混合的Ni- ^Niδ+团簇也会在二氧化铈上形成。Ni– ^Niδ+通过高角度环形暗场扫描-透射电子显微镜和能量色散X射线光谱元素标测可以观察到，簇簇高度分散在二氧化铈上。这种结构上的独特性清楚地反映在对乙氧基苯氢化成苯胺的抑制作用上，因此该催化剂显示出高的乙氧基苯选择性（92％）。相比之下，Ni金属催化剂主要产生苯胺，而NiO催化剂的活性较低。这项研究显示了如何通过调节沉积在可还原氧化物上的金属氧化物的还原程度来引导催化反应朝着亚稳中间产物的方向发展。