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Single-atom catalysts (SACs) with complete dispersion of metal species on substrates provide the ultimate atom economy and opportunities for improved heterogenous catalysis or to develop more catal...

The switch of CO

Direct oxidation of methane to methanol is a highly attractive route for upgrading methane into valued-added product. In June’s issue of Chem, Landong Li and colleagues reported a state-of-art Cu/CHA catalyst, which exhibited outstanding methanol space-time yield of 543 mmol/molCu/h with selectivity up to 91%.

Catalytic ethane dehydrogenation (EDH) to ethylene over Pt-based catalysts has received increasing interests in recent years as it is a potential alternative route to conventional steam cracking. However, the catalysts used in this reaction often suffer from rapid deactivation due to serious coke deposition and metal sintering. Herein, we reported the effects of Zn modification on the stability of Pt/Al2O3 for EDH. The Zn-modified sample (PtZn2/Al2O3) exhibits stable ethane conversion (20%) with over 95% ethylene selectivity. More importantly, it exhibits a significantly low deactivation rate of only 0.003 h−1 at 600 °C for 70 h, which surpasses most of previously reported catalysts. Detailed characterizations including in situ FT-IR, ethylene adsorption microcalorimetry, and HAADF-STEM etc. reveal that Zn modifier reduces the number of Lewis acid sites on the catalyst surface. Moreover, it could modify Pt sites and preferentially cover the step sites, which decrease surface energy and retard the sintering of Pt particle, then prohibiting the further dehydrogenation of ethylene to ethylidyne. Consequently, the good stability is realized due to anti-sintering and the decrease of coke formation on the PtZn2/Al2O3 catalyst.

The strong metal-support interaction (SMSI) has long been studied in heterogonous catalysis on account of its importance in stabilizing active metals and tuning catalytic performance. As a dynamic process taking place at the metal-support interface, the SMSI is closely related to the metal surface properties which are usually affected by the size of metal nanoparticles (NPs). In this work we report the discovery of a size effect on classical SMSI in Au/TiO2 catalyst where larger Au particles are more prone to be encapsulated than smaller ones. A thermodynamic equilibrium model was established to describe this phenomenon. According to this finding, the catalytic performance of Au/TiO2 catalyst with uneven size distribution can be improved by selectively encapsulating the large Au NPs in a hydrogenation reaction. This work not only brings in-depth understanding of the SMSI phenomenon and its formation mechanism, but also provides an alternative approach to refine catalyst performance. Strong metal-support interaction (SMSI) is critical in determining the catalytic performance of supported metal catalysts. Here the authors report a phenomenon of size-dependent classical SMSI in Au/TiO2 catalyst where larger Au particles are more prone to be encapsulated than smaller ones.

Metal atoms dispersed on the oxide supports constitute a large category of single-atom catalysts. In this review, oxide supported single-atom catalysts are discussed about their synthetic procedures, characterizations, and reaction mechanism in thermocatalysis, such as water-gas shift reaction, selective oxidation/hydrogenation, and coupling reactions. Some typical oxide materials, including ferric oxide, cerium oxide, titanium dioxide, aluminum oxide, and so on, are intentionally mentioned for the unique roles as supports in anchoring metal atoms and taking part in the catalytic reactions. The interactions between metal atoms and oxide supports are summarized to give a picture on how to stabilize the atomic metal centers, and rationally tune the geometric structures and electronic states of single atoms. Furthermore, several directions in fabricating single-atom catalysts with improved performance are proposed on the basis of state-of-the-art understanding in metal-oxide interactions.

Tuning CO2 hydrogenation selectivity to obtain targeted value-added chemicals and fuels has attracted great yet everincreasing attention. How ever, a fundamental understanding of the nature to control the selectivity is still lacking, posing a challenge in catalyst design and development. Here, w e report our new discovery in ambient pressure CO2 hydrogenation reaction where selectivity canbe completely reversed by simply changing the crystal phases of TiO2 support (anatase- or rutile-TiO2) or changing metal loadings on anatase-TiO2. Operando spectroscopy and NAP-XPS studies reveal the determining factor is dif ferent electron transfer from metal to support under reaction conditions most probably as a result of the different extents of hydrogen spillover, which changes the adsorption and activation of the intermediate of CO. Based on this new finding, we can not only regulate CO2 hydrogenation selectivity but also tune catalytic performance in other important reactions, thus opening up a door for efficient catalyst development by rational design. Fil: Li, Xiaoyu. University Of Chinese Academy Of Sciences; China. Dalian Institute Of Chemical Physics Chinese Academy Of Sciences; China Fil: Lin, Jian. Dalian Institute Of Chemical Physics Chinese Academy Of Sciences; China Fil: Li, Lin. Dalian Institute Of Chemical Physics Chinese Academy Of Sciences; China Fil: Huang, Yike. University Of Chinese Academy Of Sciences; China. Dalian Institute Of Chemical Physics Chinese Academy Of Sciences; China Fil: Pan, Xiaoli. Dalian Institute Of Chemical Physics Chinese Academy Of Sciences; China Fil: Collins, Sebastián Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Ren, Yujing. University Of Chinese Academy Of Sciences; China. Dalian Institute Of Chemical Physics Chinese Academy Of Sciences; China Fil: Su, Yang. Dalian Institute Of Chemical Physics Chinese Academy Of Sciences; China Fil: Kang, Leilei. Dalian Institute Of Chemical Physics Chinese Academy Of Sciences; China Fil: Liu, Xiaoyan. Dalian Institute Of Chemical Physics Chinese Academy Of Sciences; China Fil: Zhou, Yanliang. University Of Chinese Academy Of Sciences; China. Dalian Institute Of Chemical Physics Chinese Academy Of Sciences; China Fil: Wang, Hua. Dalian Institute Of Chemical Physics Chinese Academy Of Sciences; China Fil: Wang, Aiqin. Dalian Institute Of Chemical Physics Chinese Academy Of Sciences; China Fil: Qiao, Botao. Dalian Institute Of Chemical Physics Chinese Academy Of Sciences; China Fil: Wang, Xiaodong. Dalian Institute Of Chemical Physics Chinese Academy Of Sciences; China Fil: Zhang, Tao. Dalian Institute Of Chemical Physics Chinese Academy Of Sciences; China

Catalytic combustion is promising in removing trace amounts of CH4 to address serious environmental concerns. Supported Pd-based catalysts are most effective but often suffer from low stability in applications owing to the water-vapor-induced sintering. Herein, we develop a universal strategy to prepare irreducible-oxide-modified Pd/MgAl2 O4 catalysts which show high activity and excellent stability against both hydrothemal aging at elevated temperatures and deactivation in long-term reaction under wet conditions. The addition of irreducible oxides inhibited the deep oxidation of Pd in the oxygen-rich conditions, which preserved not only the epitaxial structure but also a suitable active phase of Pd-PdOx on MgAl2 O4 , thus promoting both activity and stability. This work provides new insights into the effect of metal-oxide interaction on CH4 combustion and offers an avenue to design hydrothermally stable and active combustion catalysts for industrial applications.

Exclusive Pt species supported on inert substrates have not achieved satisfactory performance for cryogenic CO oxidation because of the constraint of the competitive Langmuir–Hinshelwood process in...

Strong metal-support interaction (SMSI) has gained great attention in the field of heterogeneous catalysis. However, whether single-atom catalysts can exhibit SMSI remains unknown. Here, we demonstrate that SMSI can occur on TiO2 -supported Pt single atoms but at a much higher reduction temperature than that for Pt nanoparticles (NPs). Pt single atoms involved in SMSI are not covered by the TiO2 support nor do they sink into its subsurface. The suppression of CO adsorption on Pt single atoms stems from coordination saturation (18-electron rule) rather than the physical coverage of Pt atoms by the support. Based on the new finding it is revealed that single atoms are the true active sites in the hydrogenation of 3-nitrostyrene, while Pt NPs barely contribute to the activity since the NP sites are selectively encapsulated. The findings in this work provide a new approach to study the active sites by tuning SMSI.

The hydroformylation of olefins is one of the most important homogeneously catalyzed industrial reactions for aldehyde synthesis. Various ligands can be used to obtain the desired linear aldehydes in the hydroformylation of aliphatic olefins. However, in the hydroformylation of aromatic substrates, branched aldehydes are formed preferentially with common ligands. In this study, a novel approach to selectively obtain linear aldehydes in the hydroformylation of styrene and its derivatives was developed by coupling with a water-gas shift reaction on a Rh single-atom catalyst without the use of ligands. Detailed studies revealed that the hydrogen generated in situ from the water-gas shift is critical for the highly regioselective formation of linear products. The coupling of a traditional homogeneous catalytic process with a heterogeneous catalytic reaction to tune product selectivity may provide a new avenue for the heterogenization of homogenous catalytic processes.

Single-atom catalysts (SACs) have attracted extensive attention in the field of heterogeneous catalysis. However, the fabrication of SACs with high loading and high-temperature stability remains a grand challenge, especially on oxide supports. In this work, we have demonstrated that through strong covalent metal-support interaction, high-loading and thermally stable single-atom Pt catalysts can be readily prepared by using Fe modified spinel as support. Better catalytic performance in N2O decomposition reaction is obtained on such SACs than their nanocatalyst counterpart and low-surface-area Fe2O3 supported Pt SACs. This work provides a strategy for the fabrication of high-loading and thermally stable SACs for applications at high temperatures.

Single-atom catalysts (SACs) have demonstrated superior catalytic performance in numerous heterogeneous reactions. However, producing thermally stable SACs, especially in a simple and scalable way, remains a formidable challenge. Here, we report the synthesis of Ru SACs from commercial RuO2 powders by physical mixing of sub-micron RuO2 aggregates with a MgAl1.2Fe0.8O4 spinel. Atomically dispersed Ru is confirmed by aberration-corrected scanning transmission electron microscopy and X-ray absorption spectroscopy. Detailed studies reveal that the dispersion process does not arise from a gas atom trapping mechanism, but rather from anti-Ostwald ripening promoted by a strong covalent metal-support interaction. This synthetic strategy is simple and amenable to the large-scale manufacture of thermally stable SACs for industrial applications., Large scale production of thermally stable single-atom catalysts (SACs) remains challenging. Here, the authors report scalable synthesis of Ru SACs by heating physical mixture of commercial RuO2 and Fe-containing support, which is significantly promoted by strong metal-support interaction.

The functionalization of alkenes is one of the most important conversions in synthetic chemistry to prepare numerous fine chemicals. Typical procedures, such as hydrosilylation and hydroformylation, are traditionally catalyzed using homogeneous noble metal complexes, while the highly reactive and stable heterogeneous single-atom catalysts (SACs) now provide alternative approaches to fulfill these conversions by combining the advantages of both homogeneous catalysts and heterogeneous nanoparticle catalysts. In this review, the recent achievement in single-atom catalyzed hydrosilylation and hydroformylation reactions are introduced, and we highlight the latest applications of SACs for additive reactions, constructing new C-Y (Y = B, P, S, N) bonds on the terminal carbon atoms of alkenes, and then mention the applications in single-metal-atom catalyzed hydrogenation and epoxidation reactions. We also note that some tandem reactions are conveniently realized in one pot by the concisely fabricated SACs, facilitating the preparation of some pharmaceutical compounds. Lastly, the challenges facing single-atom catalysis for alkene conversions are briefly mentioned.

Semi-hydrogenation of acetylene in excess ethylene is a key industrial process for ethylene purification. Supported Pd catalysts have attracted most attention due to their superior intrinsic activity but often suffer from low selectivity. Pd single-atom catalysts (SACs) are promising to significantly improve the selectivity, but the activity needs to be improved and the feasible preparation of Pd SACs remains a grand challenge. Here, we report a simple strategy to construct Pd

Furfural is one of the most important biomass-derived chemicals. Its large-scale availability calls for the exploration of new transformation methods for further valorization. Here we report on the direct, one-step conversion of furfural into 1,4-pentanediols (1,4-PeDs) using a combination of Amberlyst-15 and Ru-FeOx/AC catalysts. It is interesting to find that the introduction of a suitable amount of FeOx results in a great improvement in the dispersion of Ru and a decrease in the Lewis acidity. Both XPS and H2-TPR show that there is electron transfer from Ru to Fe, and the electronic interaction facilitates the reduction of both Ru and Fe species. When used in combination with Amberlyst-15, the Ru-6.3FeOx/AC catalyst afforded the best performance with a 1,4-PeD yield of 86%; by contrast, Ru/AC free of FeOx only gave levulinic acid as the major product, demonstrating the key role of the acid/metal balance in the one-pot conversion of furfural to 1,4-PeD. Moreover, such a dual catalyst exhibited excellent durability within 175 h time-on-stream.

Rh1/CeO2 single-atom catalyst is highly active for CO oxidation and has the potential to serve as a multifunctional catalyst to save the usage of other noble metals in three-way catalysts. The high activity is achieved on single-atom active sites via the Mars-van Krevelen mechanism, thus avoiding CO poisoning at low temperatures.

Summary In single-atom catalysts (SACs), the isolated metal atoms on solid support are often charged. Taking advantage of this common feature, we establish ionic liquid-stabilized single-atom catalysts (ILSSACs) employing electrostatic interaction as a general stabilization strategy. While Pt nanoparticles were formed on hydroxyapatite after reaction when unprotected, Pt remained atomically dispersed on ionic liquid-stabilized samples. Density functional theory calculations reveal that the activation energy for the transformation of two isolated Pt atoms to a Pt dimer increases remarkably from 0.11 to 0.72 eV with the protection of [Bmim][BF4]. The presence of ILs also tunes the electronic state of Pt1, inducing an order-of-magnitude hydrogenation activity increase. The simple stabilization strategy is easily extended to SACs comprising various metal atom-support combinations. For instance, ILs significantly improved the stability and selectivity of a Pd1 catalyst for the hydrogenation of acetylene, thus outperforming unprotected SACs.

CO oxidation is of great importance in both fundamental study and industrial application. Supported noble metal catalysts are highly active for CO oxidation but suffer from the scarcity and high cost. Single-atom catalysts (SACs) can maximize the metal atom efficiency. Herein, ZnO nanowire (ZnO-nw) supported Rh, Au, and Pt SACs were successfully developed to investigate their CO oxidation performance. Interestingly, it was found that Rh1/ZnO-nw showed much higher activity than the other noble metals which are usually regarded as good candidates for CO oxidation. In addition, the Rh SAC possessed high stability in high-temperature CO oxidation under simulated conditions in the presence of water and hydrocarbons. The high activity and stability make Rh1/ZnO-nw promising for practical applications, especially in the automotive exhaust emission control. Theoretical calculations indicate that the CO oxidation proceeds via the Mars-van Krevelen mechanism and the lowest barrier for the rate-limiting O2 dissociation at a surface oxygen vacancy site is a key factor in determining the observed highest activity of Rh1/ZnO-nw amongst the studied SACs.

Heterogenization of the homogeneous catalysis has been studied for almost 50 years. Single-atom catalysis has the advantages of both homo- and heterogeneous catalysis. It has been proposed, and subsequently experimentally verified that single-atom catalysis is able to bridge homo- and heterogeneous catalysis, thus providing a new avenue to realize the heterogenization of homogeneous catalysis. Alkoxycarbonylation of aryl halides is an effective method for the direct synthesis of carboxylic acid derivatives, and is commonly catalyzed by Pd-based homogeneous complexes with N/P-containing ligands and organic/inorganic base. Herein, we firstly reported that Pd1/CeO2 single-atom catalyst showed good performance in the alkoxycarbonylation of aryl iodides reaction. Under base-free and ligand-free conditions, Pd1/CeO2 single-atom catalyst can transfer different aryl iodides to corresponding products. The catalyst can be easily recovered and reused four times without significant loss of reactivity.

Monodisperse gold particles (ca. 2 nm) were prepared and deposited on various supports (SiO2, Al2O3, HAP, MgAl2O4 and MgO). The acid/base properties of supports were characterized by NH3 and CO2 sorption. The size of the gold nanoparticles spans in the 1.7–6.5 nm mean diameter range after calcination as determined from TEM measurements. The amounts of accessible surface sites were estimated by binary concentration pulse chromatography of CO with Kr adsorption. The data are in agreement with the results of CO adsorption obtained by DRIFT spectroscopy. The activities of the catalysts were compared in the oxidation of benzyl alcohol in stirred batch reactors under two different conditions: in xylene solvent with atmospheric oxygen at 60 °C (in presence and in absence of K2CO3), and in a solvent-free mixture at elevated pressure and temperature (5 bar O2, 150 °C, 5 h). The activities of catalysts in benzyl alcohol conversion are described in two variants, namely related to (i) active catalytic sites (ASNA), and (ii) number of Au atoms on the geometric surface of particles (GSNA). The activities of catalysts in xylene solvent at 60 °C were excellent, with 0.28–1.11 s−1 characteristic GSNAini values (initial reaction rates related to surface Au atoms, Ausurf) in presence of K2CO3. The observed order of activities under these conditions is Au/SiO2