Catalysis Surveys from Asia最新文献

The adsorption properties for some gas molecules (H₂, N₂, CO, NO and CO₂) on pristine and transition metal-doped h-BN monolayer are investigated by using density functional theory (DFT) calculations. In contrast with N vacancy (V_N) substrates, those with B vacancy (V_B) are more easily doped with metal atoms, among which Ti atom doping shows the lowest binding energy. For the adsorption of these gas molecules, NO is most easily adsorbed on h-BN monolayer with metal dopants, especially Pt doped system yields the lowest adsorption energy of NO. Since a NO molecule on Pt doped h-BN monolayer could not be directly decomposed into O_ads and N_ads due to the high reaction energy barrier (≈ 2.00 eV), the (NO)₂ dimmer can interact with Pt to form a five-membered ring or a four-membered ring through two different Langmuir–Hinshelwood (LH) mechanisms for NO reduction catalytic reaction, respectively. The LH1 reaction process needs to overcome relatively lower energy barriers, while the product of the LH2 mechanism has a more stable structure. For the catalytic process of CO oxidation, the remained O_ads can bind with CO and form CO₂, by overcoming a much lower energy barrier of only 0.14 eV. It seems that Pt doping can enhance the adsorb capacity of h-BN monolayer for the gas molecules and the potential catalytic activity for electrochemical reduction of NO.

As a set of photocatalyst and its co-catalyst with exceptional photo-degradation performance, rGO exhibits a conspicuous board-spectrum sensitization effect to TiO₂. It has been widely recognized by studies in the field of water treatment that, their synergistic can also markedly complement short carrier lifetime and other shortcomings of TiO₂. Over the years, research conducted on TiO₂-rGO binary composite material manifests its wide modifiable space for seeking a better degradation performance and a higher solar availability. We presents an overview study on the latest modification methods of the TiO₂-rGO binary composite material and divide them into categories. This article focuses on the four of them as follows: morphology and crystalline engineering, doping modification, semiconductor ternary combination, noble-metal decoration. Furthermore, the in-depth degradation mechanism and novel structure design of the modified TiO₂-rGO binary composite materials are reviewed. Ongoing difficulties and promising opportunities have been summarized and expected in this article, aiming to guide the design and study of the future photo-degradation nanomaterial.

Over the past couple of years, fossil fuel consumption has been increased significantly. Today the consumption of coal, natural gas, and oil is rising continuously worldwide. In contrast to fossil fuels, biofuels can be advantageous because of their eco-friendly behavior with the environment. Ethanol is the “green” substitute for gasoline, as it can be blended with gasoline or can be used for the production of lighter olefins (ethylene and propylene). Ethanol can be produced either by fermentation or by catalytic route from various sources such as sugar/starchy material, carbon dioxide, carbon monoxide, and dimethylether. The catalytic route has emerged as the better route compared to fermentation due to the requirement of a large number of crops which is generally not suitable for every country. The study of ethanol synthesis and the catalytic transformation of ethanol to lighter olefins such as ethylene and propylene is presented in this review. The effect of catalysts such as zirconia, alumina, and zeolites in the ethanol transformation to olefins has been discussed in detail.

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Cr, Fe, Ce and W doped MoVTeNbO M2 phase catalysts were synthesized and used in the selective oxidation of propylene to acrylic acid (AA). Results show that the introduction of Cr, Fe, Ce and W substantially affects the physicochemical properties and catalytic performance of MoVTeNbO-based catalysts. Un-doped catalyst consists of M2 phase and TeO₂, while Cr, Fe, Ce and W-doped catalysts are mainly composed of M2 and MoO₃. It is indicated that doping of Cr, Fe, Ce and W can restrain the formation of TeO₂, but favour the formation of MoO₃. Un-doped, Cr and W-doped catalysts display irregular-shaped particles morphology, while Fe and Ce-doped catalysts display nanosheets morphology. In addition, the valence of superficial elements of catalysts changed greatly with the doping elements. For catalytic performance, in addition to Cr, the propylene conversion of the catalyst decreases obviously with doping of other elements, probably due to the drastically reduced specific surface area with doping of Fe, Ce and W. The existence of Cr and Ce can increase the selectivity to AA at all test temperatures (360–440 ℃), while Fe and W-doped catalysts only show higher selectivity than the un-doped one at high temperature of 420 and 440 ℃. It is illustrated that the catalysts with redox ability at relatively low temperature is more favorable for the selectivity to AA. Among them, Cr-doped catalyst shows the highest selectivity (85.3%) and yield (63.5%) of AA at test temperature of 380 ℃, which are 15.3 and 7.5% higher than that of un-doped catalyst, respectively.

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The M2 phase MoVTeNbO catalysts doped with Cr, Fe, Ce and W have been synthesized. It is demonstrated that the addition of Cr improves the stability of Te⁴⁺, and Cr-doped M2 phase shows excellent catalytic performance in the selective oxidation of propylene to acrylic acid.

An acid gas stream was utilized instead of pure H₂S as feedstock in the methanol thiolation reaction with Alkali/W/γ-Al₂O₃ catalysts. The catalysts were synthesized through incipient wetness impregnation and characterized by XRD, BET, and NH₃-TPD methods. The catalytic tests were performed in a fixed-bed flow reactor for an acid gas with 12.2%mol. H₂S at atmospheric pressure, 360 °C, H₂S to methanol molar ratio of 2, and LHSV of 0.5 h⁻¹. The results were then compared with the case in which pure H₂S was used as feedstock. H₂S conversion was lower in the acid gas feed than in pure H₂S feed due to participation of catalysts in hydrocarbon reforming reactions. Cesium-promoted catalysts gave the best results. H₂S in acid gas was converted about 92.8%. The yields were reported about 87.3% and 5.5% for dimethyl sulfide and methanethiol as organosulfur products respectively. The amount of hydrogen increased by about 110% in the reactor outlet.

NiMoS supported on ZSM-5 with different Si/Al ratio, crystallite size and pore structure was prepared by incipient impregnation method and applied in 1, 3, 5-trimethylbenzene (1, 3, 5-TMB) hydrodealkylation (HDAK). The physicochemical properties of samples were characterized by XRD, FTIR, SEM, N₂ adsorption–desorption, NH₃-TPD, Py-FTIR, H₂-TPR, HRTEM and TGA. It is demonstrated that for microporous NiMoS/ZSM-5, acid amount and crystallite size of HZSM-5 are key factors affecting HDAK performance. The larger acid amount and smaller crystallite size can promote the conversion of 1, 3, 5-TMB, especially the dealkylation reaction, resulting in higher BTX yield. Compared to NiMoZ-3, mesopores in micro-mesoporous NiMoAKZ-3 are beneficial to accessibility of 1, 3, 5-TMB to NiMoS and acid sites in close proximity, and the diffusion of reactant and product molecules inside pores, thus resulting in superior HDAK performance of NiMoAKZ-3. Moreover, the reaction network of 1, 3, 5-TMB HDAK was revealed according to product distribution.

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NiMoS supported on ZSM-5 was developed for heavy aromatic hydrodealkylation (HDAK). Acid amount and crystallite size of microporous ZSM-5 are key factors affecting 1,3,5-trimethylbenzene (1,3,5-TMB) HDAK. Mesopores inside ZSM-5 facilitate accessibility of 1,3,5-TMB to NiMoS and acid sites in close proximity and improve HDAK performance.

A facile and efficient electrocatalyst for hydrogen evolution reaction (HER) to produce hydrogen is very important for future energy. In this paper, amorphous manganese–cobalt nanosheets are successfully prepared by electrospinning on a foamed nickel substrate. It is found that the manganese (Mn) introduction in manganese–cobalt composites can simultaneously enhance their electrocatalytic performances. As a result, benefitting from the 3D structure, the self-supported Mn–Co hydroxides exhibits unprecedented HER activity with a relatively low overpotential of 100 mV at 10 mA cm⁻² and has a possibility for the large-scale production of hydrogen.

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Amorphous PVP/Mn₄Co nanofibers formed by electrospinning on Ni foam (NF) has remarkable catalytic activity and stability for HER after operation for 6 h in 1 M KOH, with a low overpotential of 0.1 V at 100 mA cm⁻², a low Tafel slope of 65.4 mV dec⁻¹.

With the target to fabricate more feasible catalysts for SRM to produce hydrogen, the interaction between Ni and LaBO₃ (B = Al, Cr and Fe) perovskite supports with different B-sites has been explored. To avoid the formation of big Ni grains, the Ni loading is intentionally set as low as 2 wt%. XRD and Raman results revealed that the three LaBO₃ supports are composed of pure perovskite phase, but have differed fine crystal structures. While LaFeO₃ and LaCrO₃ can be indexed to the orthorhombic perovskite phase, LaAlO₃ can be indexed to the hexagonal phase. H₂-TPR and XPS results have validated that NiO has varied interfacial interactions with the LaBO₃ supports through partial electron transfer from the supports to Ni. As a consequence, the active metallic Ni surface areas are in the order of 2%Ni/LaAlO₃ > 2%Ni/LaCrO₃ > 2%Ni/LaFeO₃, well consistent with the reaction performance. Furthermore, by varying the B-site element, the abundance of the active surface oxygen species (mainly O₂²⁻) is varied, obeying the sequence of 2%Ni/LaCrO₃ > 2%Ni/LaAlO₃ > 2%Ni/LaFeO₃, well consistent with the anti-coking ability of the catalysts. It is discovered that the change of the fine crystal structure of LaBO₃ supports can influence the SRM performance of the 2%Ni/LaBO₃ catalysts evidently. The reaction performance of the catalysts is mainly determined by the active Ni surface area, but the anti-coking ability is majorly decided by the amount of active oxygen species.

Sulfur poisoning of catalyst is a well-known phenomenon observed during the production of syngas (CO + H₂). The presence of traces of sulfur content in the feedstock can drastically reduce the catalyst activity and life. Several measures have been developed over the years to mitigate the catalyst deactivation process due to sulfur poisoning. In this paper, we review literature from 1996-present related to all the developments made for sulfur-resistant systems. The basis of poisoning being the sulfur content in the feedstock, potential fuel-containing feedstocks for syngas production were briefly discussed. The basics of sulfur poisoning mechanisms are also summarized. Then, a framework consisting of sulfur tolerance methodologies were discussed. In particular, we have discussed: (i) catalyst development by altering catalyst composition and support systems, (ii) influence of using catalyst structures, (iii) process modifications and optimization, (iv) desulfurization techniques for removal of sulfur from feed and/or product streams, and (v) effective catalyst regeneration techniques to extend the catalyst life. This review emphasizes the integration of the best set of methods to develop sulfur tolerance strategies.