Letter pubs.acs.org/acscatalysis
Oxygen-Deficient Tungsten Oxide as Versatile and Efficient Hydrogenation Catalyst Jiajia Song,∥ Zhen-Feng Huang,∥ Lun Pan, Ji-Jun Zou,* Xiangwen Zhang, and Li Wang Key Laboratory for Green Chemical Technology of the Ministry of Education, School of Chemical Engineering and Technology, Tianjin University; Collaborative Innovative Center of Chemical Science and Engineering (Tianjin), Tianjin 300072, China S Supporting Information *
ABSTRACT: Heterogeneous hydrogenation is one of the most important industrial operations, and reduced metals (mostly noble metals and a few inexpensive metals) generally serve as the catalyst to activate molecular H2. Herein we report oxygen-deficient tungsten oxide, such as WO2.72, is a versatile and efficient catalyst for the hydrogenation of linear olefins, cyclic olefins, and aryl nitro groups, with obvious advantages compared with non-noble metal nickel catalyst from the aspect of activity and selectivity. Density functional theory calculations prove the oxygen-deficient surface activates H2 very easily in both kinetics and thermodynamics. Testing on several oxygen-deficient tungsten oxides shows a linear dependence between the hydrogenation activity and oxygen vacancy concentration. Tungsten is earth-abundant, and WO2.72 can be synthesized in large scale using a low-cost procedure, which provides an ideal catalyst for industrial application. Because oxygen vacancy is a common characteristic of many metal oxides, the findings in this work may be extended to other metal oxides and thus provide the possibility for exploring a new type of hydrogenation catalyst. KEYWORDS: heterogeneous catalysis, hydrogenation, oxygen vacancy, tungsten oxide, molecular H2 activatation
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have stable crystal phase, not just surface reduced WO3, which inspires interesting properties for new applications.18,19,21 Specifically, WO2.72 is a well-studied phase consisting of a distorted ReO3 unit where cornersharing distorted and tilt WO6 octahedra are connected in the a-, b-, and c-direction.16,19 Oxygen vacancies in metal oxide serving as shallow donors can improve the electrical conductivity and donor density and thus enhance the surface species (such as H 2 and CO 2 ) adsorption,16 suggesting great potential in H2 activation and subsequent hydrogenation. Herein, we report oxygen-deficient tungsten oxide, especially WO2.72, is a versatile and efficient catalyst for the saturation of olefins and selective transform of nitroarenes to anilines. Our first-principles computations and experiments unambiguously show the unique hydrogenation activity is governed by oxygen vacancies that can easily activate molecular H2. Also these earth-abundant oxides are synthesized using a low-cost method and thus specifically suitable for largescale application. First, using density functional theory (DFT) calculations, we demonstrated that the oxygen-deficient surface of tungsten oxide can activate H2 very easily in kinetics and thermodynamics. We computed the adsorption, activation, and dissociation of molecular H2 on three different surfaces: stoichiometric WO3 surface, WO3 surface with oxygen vacancy
eterogeneous catalytic hydrogenation is one of the most valuable synthetic transformations in chemical industry, including in petroleum refinery and processing, as well as in the manufacture of fine and bulk chemicals.1−4 In particular, hydrogenation of olefins to alkanes is a crucial step for the upgrading of petroleum streams; meanwhile, transforming substituted nitroarenes to anilines is of great importance because anilines are among the most important intermediates necessary for dyestuffs and pharmaceuticals.5−9 Molecular hydrogen activation/dissociation is the first and often ratelimiting step for the hydrogenation reaction.10−13 Heterogeneous hydrogenation catalysts often come from noble metals or their alloys because they are effective in activating H2 at modest temperature and pressure,2,3 but the high-cost and limited availability stimulates numerous efforts in seeking a cheap catalyst.7−9,14 Nickel-based catalysts are cheap and widely used; however, the hydrogenation activity needs improvement, and caution is necessary when handling this flammable metal.3 In addition, Pt, Pd, and Ni are not so selective in the hydrogenation of substituted nitroarenes.5,15 Therefore, there has been an ongoing effort to find an earth-abundant, low-cost, highly active, highly selective, and stable-in-air hydrogenation catalyst. Tungsten oxides have attracted great attention for organic synthesis, photocatalysis, and electrochemistry.16−21 A unique advantage of tungsten oxides is the nonstoichiometric property as the lattice can withstand a considerable amount of oxygen vacancies.16 Moreover, many oxygen-deficient oxides (WOx90% when prolonging the reaction time or increasing the reaction temperature (Figure 4b). Furthermore, WO2.72 performs stably in a recycling experiment, with activity loss
