Revealing the anti-sintering phenomenon on silica-supported nickel catalysts during CO_(2)hydrogenation

The CO_(2)catalytic hydrogenation represents a promising approach for gas-phase CO_(2)utilization in a direct manner.Due to its excellent hydrogenation ability,nickel has been widely studied and has shown good activities in CO_(2)hydrogenation reactions,in addition to its high availability and low price.However,Ni-based catalysts are prone to sintering under elevated temperatures,leading to unstable catalytic performance.In the present study,various characterization techniques were employed to study the structural evolution of Ni/SiO_(2)during CO_(2)hydrogenation.An anti-sintering phenomenon is observed for both 9%Ni/SiO_(2)and 1%Ni/SiO_(2)during CO_(2)hydrogenation at 400℃.Results revealed that Ni species were re-dispersed into smaller-sized nanoparticles and formed Ni^(0)active species.While interestingly,this anti-sintering phenomenon leads to distinct outcomes for two catalysts,with a gradual increase in both reactivity and CH_(4)selectivity for 9%Ni/SiO_(2)presumably due to the formation of abundant surface Ni°from redispersion,while an apparent decreasing trend of CH_(4)selectivity for 1%Ni/SiO_(2)sample,presumably due to the formation of ultra-small nanoparticles that diffuse and partially filled the mesoporous pores of the silica support over time.Finally,the redispersion phenomenon was found relevant to the H_(2)gas in the reaction environment and enhanced as the H_(2)concentration increased.This finding is believed to provide in-depth insights into the structural evolution of Ni-based catalysts and product selectivity control in CO_(2)hydrogenation reactions.

Achieving anti-sintering of supported platinum nanoparticles using a thermal management strategy

Sintering inhibition of a catalyst at high temperatures is a challenge during heterogeneous catalysis. In this paper, we report that hexagonal boron nitride(h-BN) is an optimal material for anti-sintering γ-Al_(2)O_(3)-supported Pt nanoparticles(NPs) originating from the high thermal conductivity of h-BN. The high thermal conductivity of h-BN ensures maximal heat dissipation from Pt NPs to γ-Al_(2)O_(3),thereby causing both Ostwald ripening and particle coalescence of Pt NPs to be decelerated at elevated temperatures.Inhibition of Pt NP sintering is also shown in the reducible TiO^(2-)supported Pt NPs with the help of h-BN. The proposed anti-sintering strategy using thermal management is universal, providing new insight into the design of anti-sintering materials and structures for a wide range of applications in heterogeneous catalysis.

Gold nanoparticle stabilization within tailored cubic mesoporous silica:Optimizing alcohol oxidation activity

Stabilizing gold nanoparticles（AuNPs） within a desired size range is critical to realize their promising catalytic performance in many important reactions.Herein,we investigate the anti-sintering properties of cubic mesoporous silica（FDU-12） as a function of pore entrance size.Simple adjustments to the type of organic template and reaction temperature enable the successful synthesis of FDU-12 with controllable entrance sizes（ 3,3-5 and 7 nm）.Excellent anti-sintering properties are observed for FDU-12 with a sub-5-nm entrance size（3-5 nm） over a wide loading concentration（1.0-8.3 wt%） and the AuNPs can be stabilized within a 4.5-5.0-nm range after calcination at 550 ℃in air for 5 h.Smaller entrance size（ 3 nm） prevents ingress of 3-nm AuNPs to the mesopores and results in low loading capacity and sintering.Conversely,FDU-12 possessing a larger entrance size（7 nm） shows promising anti-sintering properties at high loading concentrations,although catalytic performance is significantly lost at lower concentrations（e.g.2.1 wt%,14.2 ± 5.5 nm）.Different anti-sintering mechanisms are proposed for each of the different FDU-12 entrance sizes.Additionally,catalytic data indicates that the obtained 4.5-nm AuNPs supported on FDU-12 with a sub-5-nm entrance size exhibit excellent mass-specific activity（1544 mmol g_（Au）^（-1） h^（-1）） and selectivity（ 99%）at 230 ℃ for the gas-phase selective oxidation of cyclohexanol.

Preparation of CeO_2-Modified Mg(Al)O-Supported Pt–Cu Alloy Catalysts Derived from Hydrotalcite-Like Precursors and Their Catalytic Behavior for Direct Dehydrogenation of Propane

A series of PtCuCeMgAl quintuple hydrotalcite-like compounds with different Ce contents were synthesized by one-pot method. After calcining and reduction, CeO_2-modified Mg(Al)O-supported Pt–Cu alloy catalysts were obtained. To understand the effect of Cu and Ce, the structure and physico-chemistry properties of the catalysts were characterized and analyzed, and the catalytic behaviors were investigated in a direct dehydrogenation of propane to propene. The results show that the Pt^(4+), Cu^(2+), and Ce^(3+) ions can be incorporated into the brucite-like layers and the Ce content significantly affects the interaction strength between Pt and Cu and the dehydrogenation performance of propane. Under the reaction conditions, the highest propane conversion(45%) with 89% selectivity to propene and a 40% propene yield were achieved with a 0.3 wt% Ce-modified PtCu/Mg(Al)O catalyst. The improved catalytic performance is related to the easy formation of Pt–Cu alloy phase, excellent resistance to sintering, and coke deposits of active components modified by CeO_2.

Improvement of CO2 capture performance of calcium-based absorbent modified with palygorskite

Limestone can be used for CO_2 capture and sequestration(CCS) in flue gas effectively. However, its CCS capability will dramatically decline after several cycles due to the surface "sintering". In this work, the limestone was modified with palygorskite to reduce sintering phenomenon between the absorbent particles during the CCS process and the carbonation rate of the limestone can be enhanced effectively. Palygorskite is a natural mineral with nano-fibrous structure which can reduce the mutual contact of limestone particles during the CCS process. The results were detected by TGA, SEM, MIP, FTIR and particle size analyzer respectively. The best CO_2 capture performance of modified absorbent was 13.11% improvement with only 5 wt% palygorskite added during the CCS process after 15 cycles compared with natural absorbent. It was found that excellent microscopic structures of absorbent modified with palygorskite was created, and the surface sintering was postponed leading to CO_2 capture performance enhanced under the same conditions.

Pt nanocrystallines/TiO_2 with thickness-controlled carbon layers:Preparation and activities in CO oxidation

In this work, a series of Pt nanocrystallines（Pt NCs） supported on TiO2 substrate with controlled thickness of carbon layers（C-Pt/TiO2） were synthesized. Well-dispersed Pt NCs were facilely synthesized at room temperature by a photo-reduction process in lytropic liquid crystal（LCs）. Surface tuning of the carbon layers on Pt/TiO2 catalysts was achieved by varying the calcination atmospheres（in argon, air, and oxygen） and characterized by XPS and HRTEM. The influence of the coated carbon layers on the catalytic activity of catalysts is investigated by CO oxidation reaction which presented the following ranks： C-Pt/TiO2-O2〉 C-Pt/TiO2-Air 〉 C-Pt/TiO2-Ar. It is found that the carbon layer coating can stabilize the Pt NCs and enable them anti-sintering at high temperature. This finding provides new insight into understanding the C-Pt/TiO2 ternary system for tuning their catalytic performance.

Promoted porous Co_3O_4-Al_2O_3 catalysts for ammonia decomposition

Transition metal catalysts have been considerably used for NH3 decomposition because of the potential application in COx-free H2 generation for fuel cells. However, most transition metal catalysts prepared via traditional synthetic approaches performed the inferior stability due to the agglomeration of active components. Here, we adopted an efficient method, aerosol-assisted self- assembly approach （AASA）, to prepare the optimized cobalt-alumina （C0304-A1203） catalysts. The C0304-A1203 catalysts exhibited excellent catalytic performance in the NH3 decomposition reaction, which can reach 100% conversion at 600 ℃and maintain stable for 72 h at a gaseous hourly space velocity （GHSV） of 18000 cm3 gcat-1 h-1. The catalysts were characterized by various techniques including transmission electron microscope （TEM）, scanning electron microscope （SEM）, nitrogen sorption, temperature-programmed reduction by hydrogen （H2-TPR）, ex-situ/in-situ Raman and ex-situ/in-situ X-ray diffraction （XRD） to obtain the information about the structure and property of the catalysts. H2-TPR and in-situ XRD results show that there is strong interaction between the cobalt and alumina species, which influences the redox properties of the catalysts. It is found that even a low content of alumina （10 at%） is able to stabilize the catalysts due to the adequate dispersion and rational interaction between different components, which ensures the high activity and superior stability of the cobalt-alumina catalysts.

Tuned single atom coordination structures mediated by polarization force and sulfur anions for photovoltaics

Impeding high temperature sintering is challengeable for synthesis of carbon-supported single-atom catalysts (C-SACs), which requires high-cost precursor and strictly-controlled procedures. Herein, by virtue of the ultrastrong polarity of salt melts, sintering of metal atoms is effectively suppressed. Meanwhile, doping with inorganic sulfur anions not only produces sufficient anchoring sites to achieve high loading of atomically dispersed Co up to 13.85 wt.%, but also enables their electronic and geometric structures to be well tuned. When served as a cathode catalyst in dye-sensitized solar cells, the C-SAC with Co-N4-S2 moieties exhibits high activity towards the iodide reduction reaction (IRR), achieving a higher power conversion efficiency than that of conventional Pt counterpart. Density function theory (DFT) calculations revealed that the superior IRR activity was ascribed to the unique structure of Co-N4-S2 moieties with lower reaction barriers and moderate binding energy of iodine on the Co center, which was beneficial to I2 dissociation.