Dual active sites over Cu-ZnO-ZrO2 catalysts for carbon dioxide hydrogenation to methanol.

CO2 hydrogenation to methanol is a significant approach to tackle the problem of global warming and simultaneously meet the demand for the portable fuel. Cu-ZnO catalysts with various kinds of promoters have received wide attention. However, the role of promoter and the form of active sites in CO2 hydrogenation are still in debate. Here, various molar ratios of ZrO2 were added into the Cu-ZnO catalysts to tune the distributions of Cu0 and Cu+ species. A volcano-like trend between the ratio of Cu+/ (Cu+ + Cu0) and the amount of ZrO2 is presented, among which the CuZn10Zr (the molar ratio of ZrO2 is 10%) catalyst reaches the highest value. Correspondingly, the maximum value of space-time yield to methanol with 0.65 gMeOH/(gcat·hr) is obtained on CuZn10Zr at reaction conditions of 220°C and 3 MPa. Detailed characterizations demonstrate that dual active sites are proposed during CO2 hydrogenation over CuZn10Zr catalyst. The exposed Cu0 takes participate in the activation of H2, while on the Cu+ species, the intermediate of formate from the co-adsorption of CO2 and H2 prefers to be further hydrogenated to CH3OH than decomposing into the by-product of CO, yielding a high selectivity of methanol.

Atomic Pyridinic Nitrogen Sites Promoting Levulinic Acid Hydrogenations over Double-Shelled Hollow Ru/C Nanoreactors.

Nitrogen-doped nanocarbons are widely used as supports for metal-heterogeneous catalytic conversions. When nitrogen-doped nanocarbon supports are used to disperse metallic nanoparticles (MNPs), the nitrogen dopant can enhance MNPs electron density to reach higher catalytic activity and promote MNPs stability through anchoring effects. However, the precise identification of active nitrogen species between N-dopants and reactants is rarely reported. Herein, a proof-of-concept study on the active N species for levulinic acid hydrogenation is reported. A double-shell structured carbon catalyst (DSC) is designed with selectively locating ultrafine Ru NPs only on inner carbon shell, specifically, different N species on the external carbon shell. Through the design of such a nanostructure, it is demonstrated that the alkaline pyridinic N species on the outer shell serves as an anchor point for the spontaneous binding of the acidic reactant. The pyridinic N content can be modulated from 7.4 to 29.2 mg gcat-1 by selecting different precursors. Finally, the Ru-DSC-CTS (using chitosan as the precursor) catalyst achieves a 99% conversion of levulinic acid under 70 °C and 4 MPa hydrogen pressure for 1 h. This work sheds light on the design of nanoreactors at the atomic scale and investigates heterogeneous catalysis at the molecular level.

Fabrication of Efficient Hydrogenation Nanoreactors by Modifying the Freedom of Ultrasmall Platinum Nanoparticles within Yolk-Shell Nanospheres.

The synthesis of silica-based yolk-shell nanospheres confined with ultrasmall platinum nanoparticles (Pt NPs) stabilized with poly(amidoamine), in which the interaction strength between Pt NPs and the support could be facilely tuned, is reported. By ingenious utilization of silica cores with different surface wettability (hydrophilic vs. -phobic) as the adsorbent, Pt NPs could be confined in different locations of the yolk-shell nanoreactor (core vs. hollow shell), and thus, exhibit different interaction strengths with the nanoreactor (strong vs. weak). It is interesting to find that the adsorbed Pt NPs are released from the core to the hollow interiors of the yolk-shell nanospheres when a superhydrophobic inner core material (SiO2 -Ph) is employed, which results in the preparation of an immobilized catalyst (Pt@SiO2-Ph); this possesses the weakest interaction strength with the support and shows the highest catalytic activity (88 500 and 7080 h(-1) for the hydrogenation of cyclohexene and nitrobenzene, respectively), due to its unaffected freedom of Pt NPs for retention of the intrinsic properties.

Sustainable Carbon Materials toward Emerging Applications.

It is desirable for a sustainable society that the production and utilization of renewable materials are net-zero in terms of carbon emissions. Carbon materials with emerging applications in CO2 utilization, renewable energy storage and conversion, and biomedicine have attracted much attention both academically and industrially. However, the preparation process of some new carbon materials suffers from energy consumption and environmental pollution issues. Therefore, the development of low-cost, scalable, industrially and economically attractive, sustainable carbon material preparation methods are required. In this regard, the use of biomass and its derivatives as a precursor of carbon materials is a major feature of sustainability. Recent advances in the synthetic strategy of sustainable carbon materials and their emerging applications are summarized in this short review. Emphasis is made on the discussion of the original intentions and various sustainable strategies for producing sustainable carbon materials. This review provides basic insights and significant guidelines for the further design of sustainable carbon materials and their emerging applications in catalysis and the biomedical field.

Generalized reactivity descriptor of defective carbon catalysts for acetylene hydrochlorination: the ratio of sp2 : sp3 hybridization.

The golden section point in carbon catalysts for acetylene hydrochlorination has been determined. The surface sp2 : sp3 ratio of two types of carbon catalysts, including nanodiamond- and graphite-oriented carbons, both have a volcano relationship with the catalytic performance for acetylene hydrochlorination, and the optimized ratios are both around 32-35%.

Constructing and controlling ruthenium active phases for acetylene hydrochlorination.

Ru-Based catalysts with distinct active phases from Ru0, to RuO2, RuCl3 and RuCl2N were synthesized and evaluated in acetylene hydrochlorination. RuCl2N is identified as the efficient active phase due to its co-activation of acetylene and hydrogen chloride. This discovery holds great potential to accelerate the large-scale application of Ru-based catalysts in industry.

Defective graphene@diamond hybrid nanocarbon material as an effective and stable metal-free catalyst for acetylene hydrochlorination.

A defective nanodiamond-graphene material (ND@G) exhibits superior catalytic activity in acetylene hydrochlorination with an acetylene conversion of 50%, selectivity to vinyl chloride of up to 99.5% at 220 °C, and a C2H2 gas hourly space velocity of 300 h-1, which is the first example of a metal-free catalyst with comparable performance to that of the 0.25% Au/C catalyst.

Effect of nitrogen co-doping with ruthenium on the catalytic performance of Ba/Ru-N-MC catalysts for ammonia synthesis.

Nitrogen co-doping with ruthenium mesoporous carbons (Ru-N-MC) was prepared by co-impregnation of sucrose and urea on a RuCl3/SiO2 template followed by a thermal carbonization process. The turnover frequency (TOF) of the Ba/Ru-N-MC catalyst in ammonia synthesis is 0.16 s-1 under reaction conditions of 400 °C, pressure of 10 MPa and space velocity of 10 000 h-1. The superior catalytic performance of the Ba/Ru-N-MC is proposed to originate from the strong metal-support interaction between Ru nanoparticles (NPs) and carbon support. In addition to the activity, the Ba/Ru-N-MC catalyst exhibits a long-term stability for 35 h without significant deactivation.

Wheat flour-derived N-doped mesoporous carbon extrudate as superior metal-free catalysts for acetylene hydrochlorination.

N-Doped mesoporous carbon extrudate with a major quaternary N species has been successfully prepared through direct carbonization of wheat flour/gluten with silica, which is a cheap and convenient method for scale-up production approach. The obtained carbon extrudate metal-free catalyst enables highly efficient production of vinyl chloride monomer through acetylene hydrochlorination, with a superior catalytic performance and excellent stability (>85% conversion and vinyl chloride selectivity over 99% at 220 °C).

Effect of sulfuric acid on textural properties and catalytic performance of ruthenium-containing ordered mesoporous carbon prepared via a direct RuCl3/SBA-15 hard templated method.

Ruthenium-containing ordered mesoporous carbon (Ru-OMC) catalysts with highly dispersed Ru nanoparticles semi-embedded in carbon framework were prepared via a direct RuCl3/SBA-15 hard templated method. The effect of sulfuric acid on the texture structure and catalytic performance of Ru-OMC were studied. The status of Ru nanoparticles and mesoporous structure of Ru-OMC catalysts were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), nitrogen sorption, scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and CO chemisorption techniques. The addition of appropriate amount of sulfuric acid is necessary to improve the ordered mesoporous structure of Ru-OMC catalysts. The framework of carbon structure shrinks with the increase in sulfur acid contents, which is proved by a slight decrease in surface area and increase in pore diameters for Ru-OMC with different sulfur contents. The turnover frequency (TOF) for Ru-OMC reaches the highest up to 3.98 s(-1) in benzene hydrogenation with optimized sulfur acid content of 0.08 mmol/g sucrose.

Enzyme confined in silica-based nanocages for biocatalysis in a Pickering emulsion.

The encapsulation of lipase into the nanocages of FDU-12 and the amphiphilic modification of the surfaces of FDU-12 can concurrently be accomplished via a facile silylation method. The obtained lipase-loaded FDU-12 particles featuring superior biocatalytic activity and negligible enzyme leaching can serve as efficient stabilizers for a Pickering emulsion to enhance the performance of biphasic enzymatic reactions.

Construction of porous Cu/CeO2 catalyst with abundant interfacial sites for effective methanol steam reforming.

Methanol is a promising hydrogen carrier for fuel cell vehicles (FCVs) via methanol steam reforming (MSR) reaction. Ceria supported copper catalyst has attracted extensive attentions due to the extraordinary oxygen storage capacity and abundant oxygen vacancies. Herein, we developed a colloidal solution combustion (CSC) method to synthesize a porous Cu/CeO2(CSC) catalyst. Compared with Cu/CeO2 catalysts prepared by other methods, the Cu/CeO2(CSC) catalyst possesses highly dispersed copper species and abundant Cu+-Ov-Ce3+ sites at the copper-ceria interface, contributing to methanol conversion of 66.3 %, CO2 selectivity of 99.2 %, and outstanding hydrogen production rate of 490 mmol gcat-1 h-1 under 250 °C. The linear correlation between TOF values and Cu+-Ov-Ce3+ sites amount indicates the vital role of Cu+-Ov-Ce3+ sites in MSR reaction, presenting efficient ability in activation of water. Subsequently, a deep understanding of CSC method is further presented. In addition to serving as a hard template, the colloidal silica also acts as disperser between nanoparticles, enhancing the copper-ceria interactions and facilitating the generation of Cu+-Ov-Ce3+ sites. This study offers an alternative approach to synthesize highly dispersed supported copper catalysts.