Enhanced Proximity of Rh1,2-Rhn Ensembles Encaged in UiO-67 Boosting Catalytic Conversion of Syngas to Oxygenates.

Maintaining high conversion under the premise of high oxygenates selectivity in syngas conversion is important but a formidable challenge in Rh catalysis. Monometallic Rh catalysts provide poor oxygenate conversion efficiency, and efforts have been focused on constructing adjacent polymetallic sites; however, the one-pass yields of C2+ oxygenates over the reported Rh-based catalysts were mostly <20 %. In this study, we constructed a monometallic Rh catalyst encapsulated in UiO-67 (Rh/UiO-67) with enhanced proximity to dual-site Rh1,2-Rhn ensembles. Unexpectedly, this catalyst exhibited high efficacy for oxygenate synthesis from syngas, giving a high oxygenate selectivity of 72.0 % with a remarkable CO conversion of 50.4 %, and the one-pass yield of C2+ oxygenates exceeded 25 %. The state-of-the-art characterizations further revealed the spontaneous formation of an ensemble of Rh single atoms/dimers (Rh1,2) in the proximity of ultrasmall Rh clusters (Rhn) confined within the nanocavity of UiO-67, providing adjacent Rh+-Rh0 dual sites dynamically during the reaction that promote the relay of the undissociated CHO species to the CHx species. Thus, our results open a new route for designing highly efficient Rh catalysts for the conversion of syngas to oxygenates by precisely tuning the ensemble and proximity of the dual active sites in a confined space.

Selective Hydrogenation of Dimethyl Oxalate to Methyl Glycolate over Boron-Modified Ag/SiO2 Catalysts.

The addition of boron (B) as a promoter to the Ag/SiO2 catalyst for the selective hydrogenation of dimethyl oxalate (DMO) to methyl glycolate (MG) was investigated. A comparison of the preparation method for incorporation of B found that the addition during the ammonia evaporation deposition-precipitation synthesis of the Ag/SiO2 catalyst (Ag-B/SiO2) was inferior to incipient wetness impregnation introduction of the Ag/SiO2 catalyst (B/Ag/SiO2). Moreover, the effects of B contents (0.5-5 wt %) on the physicochemical properties and catalytic performance of the B/Ag/SiO2 catalysts were investigated by XRF, N2-physisorption, XRD, FTIR, TEM, EDX mapping, H2-TPR, NH3-TPD, XPS, and catalytic testing. The results indicated that both the catalytic activity and stability of the Ag/SiO2 catalyst were noticeably enhanced after the introduction of B. The B/Ag/SiO2 catalyst with 1 wt % B showed the best catalytic performance of 100% DMO conversion and 88.3% MG selectivity, which could be attributed to the highest dispersion of the active metal and the smallest Ag particle size stabilized by the strong interaction between silver and boron species.

Ni-Modified Ag/SiO2 Catalysts for Selective Hydrogenation of Dimethyl Oxalate to Methyl Glycolate.

Ni-modified Ag/SiO2 catalysts containing 0~3 wt.% Ni were obtained by impregnating Ni species onto Ag/SiO2 followed by calcination and reduction. The catalysts' performance in the hydrogenation of dimethyl oxalate (DMO) to methyl glycolate (MG) was tested. Ag-0.5%Ni/SiO2 showed the highest catalytic activity among these catalysts and exhibited excellent catalytic stability. The effects of the Ni content on the structure and surface chemical states of catalysts were investigated by XRF, N2-sorption, XRD, TEM, EDX-mapping, FT-IR, H2-TPR, UV-vis, and XPS. The better catalytic activity and stability of Ni-modified Ag/SiO2 (versus Ag/SiO2) are ascribed to the improved dispersion of active Ag species as well as the higher resistance to the growth of Ag particles due to the presence of Ni species.

Nitrogen-doped hollow carbon spheres with tunable shell thickness for high-performance supercapacitors.

Nitrogen-doped hollow carbon spheres (NHCSs) are well prepared by using Cu2O microspheres as a hard template and 3-aminophenol formaldehyde resin polymer as carbon and nitrogen precursors. The thickness of the carbon shell can be easily controlled in the range of 15-84 nm by simply adjusting the weight ratios of the precursors to Cu2O microspheres, and the Cu2O templates can also be further reused. Physicochemical characterization demonstrates that the obtained NHCSs possess a well-developed hollow spherical structure, thin carbon shell and high nitrogen doping content. Due to these characteristics, when further utilized as electrodes for supercapacitors, the NHCSs with the carbon shell thickness of 15 nm show a high capacitance of 263.6 F g-1 at 0.5 A g-1, an outstanding rate performance of 122 F g-1 at 20 A g-1 and an excellent long-term cycling stability with only 9.8% loss after 1000 cycles at 5 A g-1 in 6 M KOH aqueous electrolyte. This finding may push forward the development of carbon materials, exhibiting huge potential for electrochemical energy storage applications.

Hepatitis B virus S gene therapy with 10-23 DNAzyme delivered by chitosan-g-stearic acid micelles.

DNAzymes have the potential to suppress gene expression through sequence-specific mRNA cleavage and can therefore play an important role in various gene therapies. Hepatitis B virus (HBV) is still one of the most serious liver infections in people around the world and is difficult to treat. We previously designed a 10-23 DNAzyme called DrzBS, which targets HBV S gene expression, but this enzyme depends on exogenous delivery, and so its application has been limited. To overcome this limitation, we have now developed a chitosan-based nanocarrier (chitosan-g-stearic acid, CSO-SA) for intracellular delivery of DrzBS, then compared the inhibition effect of our CSO-SA/DrzBS complex to a common transfection reagent, Lipofectamine™ 2000/DrzBS, on hepatitis B surface antigen expression. The synthesized CSO-SA assembles into micelles in an aqueous solution and exhibits excellent cytoplasmic targeting, and could protect DrzBS from degradation by ribonuclease. CSO-SA/DrzBS showed a higher inhibition rate (IR) than Lipofectamine™ 2000/DrzBS. Moreover, at the same DrzBS concentration (1.2 µmol L-1), the maximum IR of CSO-SA/DrzBS micelles was 2.4-fold that of the Lipofectamine™ 2000/DrzBS complex, and held on for 96 hours. Compared with Lipofectamine™ 2000/DrzBS, CSO-SA/DrzBS achieved a higher HBV inhibition effect. This study demonstrates that CSO-SA micelles can serve as a potential vector for DrzBS and that CSO-SA/DrzBS micelles are a promising application for anti-HBV gene therapy.

Enhanced resistance to calcium poisoning on Zr-modified Cu/ZSM-5 catalysts for the selective catalytic reduction of NO with NH3.

Ca/ZrCu/ZSM-5 catalysts containing different Zr contents were prepared by incipient wetness impregnation. The catalysts were tested for the selective catalytic reduction (SCR) of NO x with ammonia and characterized by N2-BET, N2O titration, XRD, NH3-TPD, H2-TPR, and XPS techniques. In the temperature range of 100-170 °C, after calcium impregnation, NO x conversion over the Cu/ZSM-5 catalyst decreased by 11.3-24.3%, while that over Zr0.10/Cu/ZSM-5 only decreased by 3.8-12.2%. The improvement of the calcium poisoning resistance of the ZrCu/ZSM-5 catalyst is mainly attributed to an increase in the dispersion and the surface concentration of Cu. Moreover, the addition of zirconium promotes the reduction of CuO by decreasing the interaction between CuO and CaO, which also contributes to the improvement of resistance to CaO poisoning. The apparent activation energy and turnover frequency for the SCR reaction over the Ca/Zr x Cu/ZSM-5 catalysts were calculated and discussed.

High-effective approach from amino acid esters to chiral amino alcohols over Cu/ZnO/Al2O3 catalyst and its catalytic reaction mechanism.

Developing the high-efficient and green synthetic method for chiral amino alcohols is an intriguing target. We have developed the Mg(2+)-doped Cu/ZnO/Al2O3 catalyst for hydrogenation of L-phenylalanine methyl ester to chiral L-phenylalaninol without racemization. The effect of different L-phenylalanine esters on this title reaction was studied, verifying that Cu/ZnO/Al2O3 is an excellent catalyst for the hydrogenation of amino acid esters to chiral amino alcohols. DFT calculation was used to study the adsorption of substrate on the catalyst, and showed that the substrate adsorbs on the surface active sites mainly by amino group (-NH2) absorbed on Al2O3, and carbonyl (C=O) and alkoxy (RO-) group oxygen absorbed on the boundary of Cu and Al2O3. This catalytic hydrogenation undergoes the formation of a hemiacetal intermediate and the cleavage of the C-O bond (rate-determining step) by reacting with dissociated H to obtain amino aldehyde and methanol ad-species. The former is further hydrogenated to amino alcohols, and the latter desorbs from the catalyst surface.

Electronic storage capacity of ceria: role of peroxide in Aux supported on CeO2(111) facet and CO adsorption.

Density functional theory (DFT+U) was used to study the adsorption of Aux (x = 1-4) clusters on the defective CeO2(111) facet and CO adsorption on the corresponding Aux/CeO2-x catalyst, in this work Aux clusters are adsorbed onto the CeO2-x + superoxide/peroxide surface. When Au1 is supported on the CeO2(111) facet with an O vacancy, the strong electronegative Au(δ-) formed is not favorable for CO adsorption. When peroxide is adsorbed on the CeO2(111) facet with the O vacancy, Aux was oxidized, resulting in stable Aux adsorption on the defective ceria surface with peroxide, which promotes CO adsorption on the Aux/CeO2-x catalyst. With more Au atoms in supported Aux clusters, CO adsorption on this surface becomes stronger. During both the Au being supported on CeO2-x and CO being adsorbed on Aux/CeO2-x, CeO2 acts as an electron buffer that can store/release the electrons. These results provide a scientific understanding for the development of high-performance rare earth catalytic materials.