Gutterød Emil Sebastian, Pulumati Sri Harsha, Kaur Gurpreet, Lazzarini Andrea, Solemsli Bjørn Gading, Gunnæs Anette Eleonora, Ahoba-Sam Christian, Kalyva Maria Evangelou, Sannes Johnny Andreas, Svelle Stian, Skúlason Egill, Nova Ainara, Olsbye Unni
Centre for Materials Science and Nanotechnology, Department of Chemistry, University of Oslo, Sem Sælandsvei 26, N-0315 Oslo, Norway.
Science Institute and Faculty of Industrial Engineering, Mechanical Engineering and Computer Science, University of Iceland, Hjardarhagi 2, VR-III, 107 Reykjavík, Iceland.
J Am Chem Soc. 2020 Oct 7;142(40):17105-17118. doi: 10.1021/jacs.0c07153. Epub 2020 Sep 24.
In catalysts for CO hydrogenation, the interface between metal nanoparticles (NPs) and the support material is of high importance for the activity and reaction selectivity. In Pt NP-containing UiO Zr-metal-organic frameworks (MOFs), key intermediates in methanol formation are adsorbed at open Zr-sites at the Pt-MOF interface. In this study, we investigate the dynamic role of the Zr-node and the influence of HO on the CO hydrogenation reaction at 170 °C, through steady state and transient isotope exchange experiments, HO cofeed measurements, and density functional theory (DFT) calculations. The study revealed that an increased number of Zr-node defects increase the formation rates to both methanol and methane. Transient experiments linked the increase to a higher number of surface intermediates for both products. Experiments involving either dehydrated or prehydrated Zr-nodes showed higher methanol and methane formation rates over the dehydrated Zr-node. Transient experiments suggested that the difference is related to competitive adsorption between methanol and water. DFT calculations and microkinetic modeling support this conclusion and give further insight into the equilibria involved in the competitive adsorption process. The calculations revealed weaker adsorption of methanol in defective or dehydrated nodes, in agreement with the larger gas phase concentration of methanol observed experimentally. The microkinetic model shows that [Zr(μ-O)] and [Zr(μ-OH)(μ-O)(OH)(HO)] are the main surface species when the concentration of water is lower than the number of defect sites. Lastly, although addition of water was found to promote methanol desorption, water does not change the methanol steady state reaction rate, while it has a substantial inhibiting effect on CH formation. These results indicate that water can be used to increase the reaction selectivity to methanol and encourages further detailed investigations of the catalyst system.
在用于CO加氢的催化剂中，金属纳米颗粒（NPs）与载体材料之间的界面对于活性和反应选择性至关重要。在含Pt NP的UiO-Zr金属有机框架（MOF）中，甲醇形成过程中的关键中间体吸附在Pt-MOF界面处开放的Zr位点上。在本研究中，我们通过稳态和瞬态同位素交换实验、HO共进料测量以及密度泛函理论（DFT）计算，研究了Zr节点在170°C下对CO加氢反应的动态作用以及HO的影响。研究表明，Zr节点缺陷数量的增加会提高甲醇和甲烷的生成速率。瞬态实验将这种增加与两种产物的更多表面中间体联系起来。涉及脱水或预水合Zr节点的实验表明，脱水Zr节点上甲醇和甲烷的生成速率更高。瞬态实验表明，这种差异与甲醇和水之间的竞争吸附有关。DFT计算和微观动力学建模支持这一结论，并进一步深入了解了竞争吸附过程中涉及的平衡。计算结果表明，甲醇在缺陷或脱水节点中的吸附较弱，这与实验观察到的甲醇在气相中的浓度较高一致。微观动力学模型表明，当水浓度低于缺陷位点数量时，[Zr(μ-O)]和[Zr(μ-OH)(μ-O)(OH)(HO)]是主要的表面物种。最后，虽然发现添加水可促进甲醇脱附，但水不会改变甲醇的稳态反应速率，而对CH的形成有显著抑制作用。这些结果表明，水可用于提高对甲醇的反应选择性，并鼓励对该催化剂体系进行进一步详细研究。
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