Bifunctional CoFe/HZSM-5 catalysts orient CO2 hydrogenation towards liquid hydrocarbons.

Converting CO2 to liquid (C5+) hydrocarbons remains a significant hurdle. Our study shows that CoFe/HZSM-5 boosts C5+ selectivity to 73.4%, up from 59% for Fe/HZSM-5. This study highlights the pivotal roles of zeolite acidity and catalyst proximity in this improvement. These insights pave the way for more effective CO2 utilization.

Engineered disorder in CO2 photocatalysis.

Light harvesting, separation of charge carriers, and surface reactions are three fundamental steps that are essential for an efficient photocatalyst. Here we show that these steps in the TiO2 can be boosted simultaneously by disorder engineering. A solid-state reduction reaction between sodium and TiO2 forms a core-shell c-TiO2@a-TiO2-x(OH)y heterostructure, comprised of HO-Ti-[O]-Ti surface frustrated Lewis pairs (SFLPs) embedded in an amorphous shell surrounding a crystalline core, which enables a new genre of chemical reactivity. Specifically, these SFLPs heterolytically dissociate dihydrogen at room temperature to form charge-balancing protonated hydroxyl groups and hydrides at unsaturated titanium surface sites, which display high reactivity towards CO2 reduction. This crystalline-amorphous heterostructure also boosts light absorption, charge carrier separation and transfer to SFLPs, while prolonged carrier lifetimes and photothermal heat generation further enhance reactivity. The collective results of this study motivate a general approach for catalytically generating sustainable chemicals and fuels through engineered disorder in heterogeneous CO2 photocatalysts.

Towards the development of the emerging process of CO2 heterogenous hydrogenation into high-value unsaturated heavy hydrocarbons.

The emerging process of CO2 hydrogenation through heterogenous catalysis into important bulk chemicals provides an alternative strategy for sustainable and low-cost production of valuable chemicals, and brings an important chance for mitigating CO2 emissions. Direct synthesis of the family of unsaturated heavy hydrocarbons such as α-olefins and aromatics via CO2 hydrogenation is more attractive and challenging than the production of short-chain products to modern society, suffering from the difficult control between C-O activation and C-C coupling towards long-chain hydrocarbons. In the past several years, rapid progress has been achieved in the development of efficient catalysts for the process and understanding of their catalytic mechanisms. In this review, we provide a comprehensive, authoritative and critical overview of the substantial progress in the synthesis of α-olefins and aromatics from CO2 hydrogenation via direct and indirect routes. The rational fabrication and design of catalysts, proximity effects of multi-active sites, stability and deactivation of catalysts, reaction mechanisms and reactor design are systematically discussed. Finally, current challenges and potential applications in the development of advanced catalysts, as well as opportunities of next-generation CO2 hydrogenation techniques for carbon neutrality in future are proposed.

Importance of the Initial Oxidation State of Copper for the Catalytic Hydrogenation of Dimethyl Oxalate to Ethylene Glycol.

Exposing a Cu-based catalyst to a suitable temperature is of great importance to optimize its hydrogenation performance, as copper is sensitive to temperature. Herein, we investigated the effect of the initial oxidation state of copper, tuned by the reduction temperature, on its catalytic performance in the hydrogenation of dimethyl oxalate (DMO) to ethylene glycol (EG) through designing a series of catalysts with different reduction temperatures (200-350 °C). Among these catalysts, the Cu/SiO2 catalyst prepared by ammonia evaporation with a hydrogen reduction process at 250 °C showed the best performance in the hydrogenation of DMO with a conversion of 100 % and a selectivity to EG higher than 95 %. The relationship between the initial oxidation state of copper and catalytic performance was well established by characterizing the physicochemical properties of the Cu/SiO2 catalysts by XRD, TEM, H2 temperature-programmed reduction, N2O adsorption, and in situ reduction Auger electron spectroscopy. The initial oxidation state of copper determined the conversion of DMO and the distribution of the products, and it could be balanced by reducing the temperature to improve the activity of the catalyst. This work provides a reference for further exploration of the mechanism and guidance for the design of catalysts for the hydrogenation of esters.

Tailored metastable Ce-Zr oxides with highly distorted lattice oxygen for accelerating redox cycles.

Ceria-based catalysts are widely used in oxidation or oxidation-reduction reactions in the field of environmental science. Their catalytic functions are determined by their ability to exchange oxygen species with oxidants. The enhancement of oxygen release is desired since it is often the rate-determining step in redox cycles. Herein, we developed a lattice oxygen distortion method to enhance oxygen activation by quenching the Ce-Zr oxide nanoparticles formed from an extremely high temperature. This process can ensure the formation of solid solutions as well as avoiding atomic rearrangement during calcination, retaining the lattice oxygen at a metastable and disordered state without vacancies. Reduction, vacuum or metal deposition will easily induce oxygen release accompanied by vacancy creation. The metastable oxides can provide about 19 times more oxygen vacancies than traditional ones in a CO atmosphere. CO oxidation rates increased with increasing Zr content from 25 to 75% and achieved a new level, which is attributed to the acceleration of oxygen circulation via promoting oxygen release and supplying plenty of oxygen vacancies for redox cycles. This strategy is expected to be applied in the design and fabrication of improved oxygen storage materials.

Dual effects of water vapor on ceria-supported gold clusters.

Atomically precise nanocatalysts are currently being intensely pursued in catalysis research. Such nanocatalysts can serve as model catalysts for gaining fundamental insights into catalytic processes. In this work we report a discovery that water vapor provokes the mild removal of surface long-chain ligands on 25-atom Au25(SC12H25)18 nanoclusters in a controlled manner. Using the resultant Au25(SC12H25)18-x/CeO2 catalyst and CO oxidation as a probe reaction, we found that the catalytic activity of cluster/CeO2 is enhanced from nearly zero conversion of CO (in the absence of water) to 96.2% (in the presence of 2.3 vol% H2O) at the same temperature (100 °C). The cluster catalysts exhibit high stability during the CO oxidation process under moisture conditions (up to 20 vol% water vapor). Water vapor plays a dual role in gold cluster-catalyzed CO oxidation. FT-IR and XPS analyses in combination with density functional theory (DFT) simulations suggest that the "-SC12H25" ligands are easier to be removed under a water vapor atmosphere, thus generating highly active sites. Moreover, the O22- peroxide species constitutes the active oxygen species in CO oxidation, evidenced by Raman spectroscopy analysis and isotope experiments on the CeO2 and cluster/CeO2. The results also indicate the perimeter sites of the interface of Au25(SC12H25)18-x/CeO2 to be active sites for catalytic CO oxidation. The controlled exposure of active sites under mild conditions is of critical importance for the utilization of clusters in catalysis.

Erratum: Directly converting CO2 into a gasoline fuel.

This corrects the article DOI: 10.1038/ncomms15174.

Directly converting CO2 into a gasoline fuel.

The direct production of liquid fuels from CO2 hydrogenation has attracted enormous interest for its significant roles in mitigating CO2 emissions and reducing dependence on petrochemicals. Here we report a highly efficient, stable and multifunctional Na-Fe3O4/HZSM-5 catalyst, which can directly convert CO2 to gasoline-range (C5-C11) hydrocarbons with selectivity up to 78% of all hydrocarbons while only 4% methane at a CO2 conversion of 22% under industrial relevant conditions. It is achieved by a multifunctional catalyst providing three types of active sites (Fe3O4, Fe5C2 and acid sites), which cooperatively catalyse a tandem reaction. More significantly, the appropriate proximity of three types of active sites plays a crucial role in the successive and synergetic catalytic conversion of CO2 to gasoline. The multifunctional catalyst, exhibiting a remarkable stability for 1,000 h on stream, definitely has the potential to be a promising industrial catalyst for CO2 utilization to liquid fuels.

Mild activation of CeO2-supported gold nanoclusters and insight into the catalytic behavior in CO oxidation.

We report a new activation method and insight into the catalytic behavior of a CeO2-supported, atomically precise Au144(SR)60 nanocluster catalyst (where thiolate -SR = -SCH2CH2Ph) for CO oxidation. An important finding is that the activation of the catalyst is closely related to the production of active oxygen species on CeO2, rather than ligand removal of the Au144(SR)60 clusters. A mild O2 pretreatment (at 80 °C) can activate the catalyst, and the addition of reductive gases (CO or H2) can enhance the activation effects of O2 pretreatment via a redox cycle in which CO could reduce the surface of CeO2 to produce oxygen vacancies-which then adsorb and activate O2 to produce more active oxygen species. The CO/O2 pulse experiments confirm that CO is adsorbed on the cluster catalyst even with ligands on, and active oxygen species present on the surface of the pretreated catalyst reacts with CO pulses to generate CO2. The Au144(SR)60/CeO2 exhibits high CO oxidation activity at 80 °C without the removal of thiolate ligands. The surface lattice-oxygen of the support CeO2 possibly participates in the oxidation of CO over the Au144(SR)60/CeO2 catalyst.

One-phase controlled synthesis of Au25 nanospheres and nanorods from 1.3 nm Au : PPh3 nanoparticles: the ligand effects.

We report the controlled synthesis of [Au25(PPh3)10(SR1)5X2](2+) nanorods (H-SR1: alkyl thiol, H-SC2H4Ph and H-S(n-C6H13)) and Au25(SR2)18 nanospheres (H-SR2: aromatic thiol, H-SPh and H-SNap) under the one-phase thiol etching reaction of the polydisperse Aun(PPh3)m parent-particles (core diameter: 1.3 ± 0.4 nm, 20 < n < 50). These as-obtained gold nanoclusters are identified by UV-vis spectroscopy and matrix-assisted laser desorption ionization mass spectrometry. Furthermore, the conversion process, from Aun(PPh3)m nanoparticles to Au25(SNap)18 nanospheres, is monitored by UV-vis spectroscopy. It is observed that the Au25(PPh3)10(SR1)5X2 nanorods cannot convert to Au25(SR)18 nanospheres in the presence of excess thiol (both the alkyl and aromatic thiol) even under thermal conditions (e.g., 55 and 80 °C), indicating that both the Au25 nanorods and nanospheres are in a stable state during the alkyl and aromatic thiol etching reactions, respectively. The two different conversion pathways (i.e., to Au25(PPh3)10(SR1)5X2 nanorods and Au25(SR2)18 nanospheres) mainly are attributed to the different electronic properties and the steric effects of the alkyl and aromatic thiol ligands. The significant ligand effect also is observed in catalytic CO oxidation. The Au25(SC2H4Ph)18/CeO2 catalyst shows catalytic activity at 80 °C and reaches up to 80.7% and 98.5% (based on CO conversion) at 100 and 150 °C, while Au25(SNap)18/CeO2 and Au25(PPh3)10(SC2H4Ph)5X2/CeO2 give rise to a low activity at 100 °C with only 3.3% and 10.2% CO conversion and 98.0% and 94.6% at 150 °C.

CeO2-supported Au38(SR)24 nanocluster catalysts for CO oxidation: a comparison of ligand-on and -off catalysts.

The catalytic properties of atomically precise, thiolate-protected Au38(SR)24 (R = CH2CH2Ph) nanoclusters supported on CeO2 were investigated for CO oxidation in a fixed bed quartz reactor. Oxygen (O2) thermal pretreatment of Au38(SR)24/CeO2 at a temperature between 100 and 175 °C largely enhanced the catalytic activity, while pretreatment at higher temperatures (>200 °C) for removing thiolate instead gave rise to a somewhat lower activity than that for 175 °C pretreatment, and the ligand-off clusters were also found to be less stable. The CO conversion in the case of wet feed-gas (i.e. the presence of H2O vapor) was appreciably higher than the case of dry feed-gas when the reaction temperature was kept relatively low (between 60 and 80 °C), and interestingly the ligand-on and ligand-off catalysts exhibited opposite response to water vapor. Finally, we discussed some insights into the catalytic reaction involving the well-defined gold nanocluster catalyst.

CO oxidation catalyzed by oxide-supported Au25(SR)18 nanoclusters and identification of perimeter sites as active centers.

In this work, we explore the catalytic application of atomically monodisperse, thiolate-protected Au(25)(SR)(18) (where R = CH(2)CH(2)Ph) nanoclusters supported on oxides for CO oxidation. The solution phase nanoclusters were directly deposited onto various oxide supports (including TiO(2), CeO(2), and Fe(2)O(3)), and the as-prepared catalysts were evaluated for the CO oxidation reaction in a fixed bed reactor. The supports exhibited a strong effect, and the Au(25)(SR)(18)/CeO(2) catalyst was found to be much more active than the others. Interestingly, O(2) pretreatment of the catalyst at 150 °C for 1.5 h significantly enhanced the catalytic activity. Since this pretreatment temperature is well below the thiolate desorption temperature (~200 °C), the thiolate ligands should remain on the Au(25) cluster surface, indicating that the CO oxidation reaction is catalyzed by intact Au(25)(SR)(18)/CeO(2). We further found that increasing the O(2) pretreatment temperature to 250 °C (above the thiolate desorption temperature) did not lead to any further increase in activity at all reaction temperatures from room temperature to 100 °C. These results are in striking contrast with the common thought that surface thiolates must be removed-as is often done in the literature work-before the catalyst can exert high catalytic activity. The 150 °C O(2)-pretreated Au(25)(SR)(18)/CeO(2) catalyst offers ~94% CO conversion at 80 °C and ~100% conversion at 100 °C. The effect of water vapor on the catalytic performance is also investigated. Our results imply that the perimeter sites of the interface of Au(25)(SR)(18)/CeO(2) should be the active centers. The intact structure of the Au(25)(SR)(18) catalyst in the CO oxidation process allows one to gain mechanistic insight into the catalytic reaction.

Influences of precipitate rinsing solvents on Ni catalyst for methane decomposition to CO(x)-free hydrogen.

Influences of precipitate rinsing solvents on Ni for methane decomposition to CO(x)-free hydrogen has been investigated in this study. Calcination of nickel hydroxide precipitates rinsed by ethanol leads to the formation of nanosheet needle-like NiO, whereas calcination of those rinsed by deionized water leads to the formation of pure nanosheet NiO. When compared to Ni catalyst (Ni-et) reduced from nanosheet needle-like NiO, Ni catalyst (Ni-etwt), reduced from pure nanosheet-like NiO, exhibits a better catalytic performance for methane decomposition. Among the different rinsing processes, nickel hydroxide precipitates, rinsed first by ethanol and subsequently by deionized water, were calcined to the most suitable nanosheet NiO, which could be reduced to Ni-etwt catalyst with the highest catalytic performance of methane decomposition. A total of 1954 mol(H2)/mol(Ni) of hydrogen yields could be obtained over Ni-etwt under suitable reaction conditions. Characterization results indicate that Ni-etwt with the higher catalytic activity has the approximately 34 nm of average particle size.