Preparation Of High-performance Catalysts Research Articles

N-doped hollow carbon nanospheres anchored Pd NPs for mild selective hydrodeoxygenation of bio-models

Hydrodeoxygenation (HDO) is a promising approach for the synthesis of renewable fuels and chemicals, while the design and preparation of high-performance catalysts in this field remain a challenge. Herein, a series of hollow carbon nanospheres anchored Pd nanoparticles (NPs) catalysts with different nitrogen doping contents (Pd/HCAFR-X, X=0.3, 0.6, 0.9) were prepared for the selective HDO of bio-models compound under mild conditions. Notably, the Pd/HCAFR-0.6 catalyst exhibited excellent catalytic performance for the acetophenone (APh) HDO in polymethylhydrosiloxane (PMHS) at 50 °C for 3 h, and the yield of ethylbenzene was close to 99%. The good catalytic results can be mainly attributed to the unique hollow carbon nanospheres with abundant defects provided by appropriate nitrogen doping content. The large surface area and hierarchical porous structure of the hollow carbon framework offered more active sites, which promoted the transportation of species on the catalyst. In addition, the nitrogen doping amount can adjust the defect degree of the hollow carbon nanospheres, stabilize the dispersion and anchoring of Pd NPs, and then induce the transfer of local electrons. Furthermore, the Pd/HCAFR-0.6 catalyst showed good catalytic performance for bio-models compound HDO after 5 cycles.

Non-precious metal MoO2 co-catalysts efficiently enhance hydrogen production of ZnIn2S4 under visible light

Photogenerated electron-hole separation and transfer and band gap modulation are the main reasons for the performance of semiconductor catalysts. These problems can be effectively solved by the proper use of co-catalysts. However, the current co-catalysts are generally noble metal co-catalysts, which cannot be used industrially because of their high cost. Therefore, it is important to use non-noble metal co-catalyst to solve these problems. In this study, MoO2 with localized surface plasmon resonance (LSPR) effect loaded onto ZnIn2S4 (ZIS) by primary hydrothermal method and structured to form type II heterojunctions. The formation of the heterojunctions not only tunes the band gap to improve the light absorption intensity, but also reduces the charge transfer resistance and promotes electron-hole directed movement to improve the electron-hole separation efficiency. The tuning of the band gap and the increase in the electron-hole separation rate lead to improved performance of all ZIS/MoO2 heterojunctions under visible light (λ ≥ 420 nm). Among them, ZIS/MoO2-4% has the best photocatalytic performance of 2.757 mmol g−1 h−1, which is 3.75 times higher than that of pure ZIS (0.736 mmol g−1 h−1). This study provides a new strategy for the preparation of high performance catalysts without precious metals.

Electrochemical nitrate reduction to produce ammonia integrated into wastewater treatment: Investigations and challenges

Nitrate (NO3−) is widely found in wastewater, which is harmful to human health and water environmental. Electrochemical reduction can convert NO3− to high value-added ammonia (NH3)/ammonium (NH4+) for pollutant removal and resource recovery. Currently, electrochemical nitrate reduction to produce ammonia (ENRA) is mostly focused on the preparation of high-performance catalysts, while ignoring the prerequisite for industrial application as the stable operation and optimal regulation of the process. Therefore, the review focused on wastewater treatment, based on the mechanism of electrochemical nitrate reduction for ammonia production and reactor construction (reactor, power supply system), then summarized the operation control strategies (such as reduction potential, nitrate concentration, inorganic ions, pH) that should be noted for ENRA. Finally, the challenges (system structure, economy) and prospects (ammonia recovery process, construction of large-scale ENRA system, application of real wastewater) of the field as it moves towards commercialization were discussed. It is hoped that this review will facilitate the scaling up of ENRA in the wastewater treatment field.

Experimental and numerical study regarding the biomimetic bone porous structure to match energy and mass flow in a solar thermochemical reactor

In the methane dry reforming driven by concentrated solar energy, the challenges that restrict efficient solar energy conversion mainly include regulating the solar energy to match the solar thermochemical reaction on-demand, optimization of catalytic carrier structures and preparation of high-performance catalysts. The mismatch between energy and flow in a thermochemical reactor has important consequences for solar energy storage efficiency. To improve the solar thermochemical performance, the idea of using a biomimetic bone porous structure as a catalyst carrier is proposed to achieve flow and energy matching in a thermochemical reactor. The methods of Monte Carlo ray tracing and user-defined functions are used to establish thermochemical analysis model. A solar heat flux experimental system is built to determine the real concentrated solar heat flux. The effects of different pore size combinations and Gaussian-like inlet flow on the methane reforming performance are studied. The experiment system obtains a uniform light spot of 40 mm at Pe = 7.0 kW with the peak flux density of 3086.73 kW/m2. The results indicate that by the introduction of a biomimetic bone porous structure to optimize flow and energy matching, the energy storage efficiency and methane conversion rate can be improved by 2.17 % and 8.97 %, respectively. This research provides a novel approach for efficient solar energy conversion and storage in solar thermochemical reactor.

Metal-Acid Bifunctional Catalysts toward Tandem Reaction: One-Step Hydroalkylation of Benzene to Cyclohexylbenzene.

The one-step hydroalkylation of benzene to cyclohexylbenzene (CHB) is a technically challenging and economically interesting reaction with great industrial importance, where bifunctional catalysts play a crucial role in such a tandem reaction. In this work, we report H3PW12O40 (HPW) modified Ni nanoparticles (NPs) supported on mixed metal oxides (Ni/MMOs), which are featured by HPW species localized on the surface of Ni NPs (denoted as HPW-Ni/MMOs). The optimal catalyst (0.3HPW-Ni/MMOs) exhibits a satisfactory catalytic performance toward benzene hydroalkylation to CHB with a CHB yield of up to 41.2%, which is the highest standard among previously reported catalysts to date. A combination investigation based on HR-TEM, XPS, XANES, and in situ FT-IR verified the electron transfer from the W atom to the adjacent Ni atom, which facilitated the formation and desorption of cyclohexene (CHE) from Ni followed by the alkylation reaction of benzene and CHE at the interfacial Brønsted (B) acid sites of HPW, accounting for the significantly enhanced catalytic behavior. It is proposed that the HPW-Ni interface structure in xHPW-Ni/MMOs samples provides unique adsorption sites for benzene and CHE with a moderate adsorption strength, which serve as the intrinsic active center for this reaction: the Ni site promotes the hydrogenation of benzene to CHE, while the B acid site in HPW facilitates the alkylation of CHE and benzene to produce CHB. This work provides a fundamental understanding of the metal-acid synergistic catalysis toward the hydroalkylation reaction, which can be extended to the design and preparation of high-performance catalysts used in tandem reactions.

Electrochemical Reduction of Carbon Dioxide to Ethanol: An Approach to Transforming Greenhouse Gas to Fuel Source

Converting carbon dioxide (CO2 ) into high-value fuels or chemicals is considered as a promising way to utilize CO2 and alleviate the excessive greenhouse gas emission. Among multiple catalysis approaches, electrochemical reduction of CO2 to ethanol has an important prospect due to the high energy density and widely applications of ethanol. In recent years, many electrocatalysts for CO2 reduce reaction (CO2 RR) have shown promising catalytic activity for ethanol production. In this review, we will introduce the recent progress in this field. The basic principles and electrochemical performances of CO2 RR are reviewed at first. Then, several categories of active electrocatalysts for CO2 RR to ethanol are summarized, including the discussion of reaction mechanism and catalytic sites. Finally, several possible strategies are proposed, providing guidance for future design and preparation of high-performance catalysts.

Facile fabrication of three-dimensional porous CuFe2O4 cages as highly efficient and recyclable heterogeneous catalyst

The design and preparation of high-performance catalysts with high catalytic activity and excellent durability that are both environmentally benign and cost-effective remains a considerable challenge. Herein, a facile strategy is reported for the fabrication of three-dimensional porous CuFe2O4 cages, shortly as 3D CuFe2O4@C, by bubbling oxygen produced in situ through a CuFe2O4 suspension, followed by thermal treatment in nitrogen atmosphere. The 3D CuFe2O4@C structure increases the surface area of CuFe2O4 and provides a porous support structure. It is proposed to be a key in preventing the aggregation of CuFe2O4 during practical use. 3D CuFe2O4@C is shown to be a highly active catalyst, not only for the hydrogenation of p-nitrophenol, but also for the reduction of methylene blue in aqueous medium. 3D CuFe2O4@C exhibits remarkable catalytic activity towards p-nitrophenol reduction, with a catalytic rate constant of 2.167min−1 that is 5.35 times higher than that with pristine CuFe2O4 (0.405min−1). In addition, the 3D CuFe2O4@C catalyst has a high saturation magnetization of 51.9emug−1, indicating that it can be easily recycled using a magnet. The 3D porous metal oxide nanostructure shows promising potentials as candidates for the remediation of contaminated aquatic environments and meets the demands for addressing future environmental issues.

Ce-incorporation in mixed oxides obtained by the self-combustion method for the preparation of high performance catalysts for the CO2 reforming of methane

Abstract Ce-incorporation in Ni–Mg–Al mixed oxides obtained by the self-combustion method was followed by the preparation of high performance catalysts for the CO2 reforming of methane. The morphological, textural and structural characteristics and basic properties were determined. The mixed oxides were precursors of Ni0 nano-particles less than 10 nm, and they were partially reconstructed by the CeO2-incorporation without a morphological change. The self-combustion method improves the surface areas and basicity of the co-precipitation method. Catalysts with higher activities and selectivities and reduced coke formation were achieved by the self-combustion method. H2/CO ratios between 0.8 and 1.1 were obtained which are suitable for further applications.

State of the art in the development of biomimetic oxidation catalysts

Work during the last decade laid down the basis for biomimetic oxidation catalysis, which has become an established technique. Preliminary work relied on the use of metal complexes of 5,10,15,20-tetrakisphenylporphyrin (TPP), but these proved to be inadequate to perform the catalytic function. Further, derivatives of TPP with suitable and adequately positioned substituents, allowed the preparation of high performance catalysts, in terms of catalytic efficiency and stability, for some selected oxidations under specific reaction conditions and for a diversity of oxygen donors. The first oxidations were achieved using the ‘special’ oxygen donor iodosylbenzene, but cheaper and generally available oxidants such as sodium hypochlorite or hydrogen peroxide are presently used as the oxidants. Catalysts capable of promoting stereoselective catalysis are reported. Conditions for the efficient use of the catalysts so far reported require particular specificities and the catalytic activity is only shown, in the majority of the reported works, in the presence of selected species to act as axial ligands to the metal ion of the catalyst. Specific porphyrin structures were reported where the addition of a specific axial ligand can be avoided.