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Olefin polymerization is one of the most important chemical reactions in industry. This work presents a strategy that emphasizes the synergistic meta/para-steric hindrance of N-aryl groups and electronic effects in newly synthesized neutral salicylaldiminato nickel catalysts. These nickel(II) catalysts exhibit exceptional thermostability, ranging from 30 °C to 130 °C, demonstrating enhanced catalytic activities and broadly regulated polyethylene molecular weights (3–341 kg·mol−1) and controlled polymer branch density (2–102 brs/1000C). The preferred catalyst Ni3 with concerted steric and electronic effects enables the production of solid-state semi-crystalline polyethylene materials at temperatures below 90 °C. Notably, Ni3 exhibits an impressive tolerance of 110 °C and can withstand even the challenging polymerization temperature of 130 °C, leading to the production of polyethylene wax and oil. Also, functionalized polyethylene is produced. [ABSTRACT FROM AUTHOR]

Context: This study investigates the ethylene insertion reaction mechanism for polymerization catalysis, aiming to discern differences between Ni-α-imine ketone–type catalyst and their SiO2-supported counterpart. The reaction force analysis unveils a more intricate mechanism with SiO2 support, shedding light on unexplored factors and elucidating the observed lower catalytic activity. Furthermore, reactivity indexes suggest earlier ethylene activation in the supported catalyst, potentially enhancing overall selectivity. Finally, the reaction electronic flux analysis provides detailed insights into the electronic activity at each step of the reaction mechanism. In sum, this study offers a comprehensive understanding of the ethylene insertion reaction mechanism in both molecular and supported catalysts, underscoring the pivotal role of structural and electronic factors in catalytic processes. Methods: Density functional theory (DFT) calculations were conducted using the ωB97XD functional and the 6–31 + G(d,p) basis sets with Gaussian16 software. Computational techniques utilized in this study encompassed the IRC method, reaction force analysis, and evaluation of electronic descriptors such as electronic chemical potential, molecular hardness, and electrophilicity reactivity indexes. Additionally, reaction electronic flux analysis was employed to investigate electronic activity along the reaction coordinate. [ABSTRACT FROM AUTHOR]

The aim of this study was to deposit a Ni–La–Zr catalyst on a FeCrAl monolith by in situ growth of the catalyst on a metallic surface through immersion in a modified polymeric precursor solution. The prepared monolith was characterized by X-ray diffraction, atomic force microscopy, and scanning electron microscopy and was tested in a tri-reforming reaction of simulated biogas (CH4/CO2 = 3) for synthesis gas production. The monolithic catalyst presented better stability than the powdered catalyst under the 50-h test. In contrast, the powdered catalyst showed more pronounced deactivation, which was associated with higher carbon deposition. This study provides valuable information on a simple deposition method for Ni-based catalysts on FeCrAl monoliths for biogas tri-reforming reactions, which could have implications for biogas upgrading. [ABSTRACT FROM AUTHOR]

This study investigates the effect of cerium–zirconium supported nickel catalyst (Ni/CeZr(x)) on the dry reforming reaction of methane (CH4) and carbon dioxide (CO2) to produce hydrogen (H2) and carbon monoxide (CO) for use in petrochemical processes. CeZr supports were synthesized via template-assisted co-precipitation using CTAC as a template with varying pH values (5, 7, 8.5, and 10) and underwent hydrothermal processing. Nickel (10% by weight) was then loaded onto the support through incipient wetness impregnation. The dry reforming reaction was performed at 700 °C. Results revealed that as the pH increased from acidic to basic conditions, the precipitation and integration of ZrO2 and CeO2 improved, leading to the formation of CeZr(x) composite supports. The Ce/Zr ratio in Ni/CeZr(x) catalysts influenced the generation of oxygen vacancies (OV) on the catalyst surface, affecting CO2 and CH4 conversions and the H2/CO ratio. The Ni/CeZr(8.5) catalyst exhibited the highest activity and stability due to its high surface oxygen vacancy and the number of basic sites on the CeZr(8.5) surface. Moreover, this catalyst reduced coke formation by promoting CO2 adsorption and dissociation, which facilitated the formation of surface-bound oxygen species that reacted with the surface carbon species. [ABSTRACT FROM AUTHOR]

Syngas can be produced from biomethane via Partial Oxidation of Methane (POM), being an attractive route since it is ecofriendly and sustainable. In this work, catalysts of Ni supported on MgO–ZrO2 solid solutions, prepared by a one-step polymerization method, were characterized by HRTEM/EDX, XRD, XPS, H2-TPR, and in situ XRD. All catalysts, including Ni/ZrO2 and Ni/MgO as reference, were tested for POM (CH4:O2 molar ratio 2, 750 ºC, 1 atm). NiO/MgO/ZrO2 contained two solid-solutions, MgO–ZrO2 and NiO-MgO, as revealed by XRD and XPS. Ni (30 wt%) supported on MgO–ZrO2 solid solution exhibited high methane conversion and hydrogen selectivity. However, depending on the MgO amount (0, 4, 20, 40, 100 molar percent) major differences in NiO reducibility, growth of Ni0 crystallite size during H2 reduction and POM, and in carbon deposition rates were observed. Interestingly, catalysts with lower MgO content achieved the highest CH4 conversion (~ 95%), high selectivity to H2 (1.7) and CO (0.8), and low carbon deposition rates (0.024 g carbon.gcat−1 h−1) with Ni4MgZr (4 mol% MgO) turning out to be the best catalyst. In situ XRD during POM indicated metallic Ni nanoparticles (average crystallite size of 31 nm), supported by MgO–ZrO2 solid solution, with small amounts of NiO–MgO being present as well. The presence of MgO also influenced the morphology of the carbon deposits, leading to filaments instead of amorphous carbon. A combustion-reforming mechanism is suggested and using a MgO–ZrO2 solid solution support strongly improves catalytic performance, which is attributed to effective O2, CO2 and H2O activation at the Ni/MgO–ZrO2 interface. [ABSTRACT FROM AUTHOR]

Rate-controlled growth of carbon nanotubes (CNTs) and catalyst design are considered efficient ways for the preparation of CNTs with specific structures and properties. However, due to the difficulties in capturing the growth process of the CNTs with tiny size under a complex growth environment, the growth kinetics of CNTs and their correlation with the catalyst seed have been seldom revealed. Here, we investigated the growth process of CNTs from Ni nanoparticles (NPs) in real-time under atmospheric pressure using transmission electron microscopy equipped with a closed gas cell. It was found that the growth rates of CNTs fluctuated, and a phase transition from Ni3C to Ni, and a reshaping of the catalyst NPs occurred during the growth process. We demonstrated that CNTs dynamically interacted with the connected catalyst NPs and the fluctuated growth rates of CNTs were correlated with the structure change of catalyst NPs. The origin of the growth rate fluctuation is attributed to the change of carbon concentration gradient in catalyst NPs. [ABSTRACT FROM AUTHOR]

Catalytic methane (CH4) dry reforming (MDR) reaction proceeds with the formation of carbon; hence the effects of the catalyst preparation method on the type of carbon are worth investigating. This study investigated the performance of 20 wt% nickel praseodymium (III) oxide (20 wt% Ni/Pr2O3) catalysts prepared by incipient wetness impregnation (IWI), ultrasonic wet impregnation (US-WI), and Pechini sol–gel (PSG) methods. The catalysts crystallite size was approximately 21.3 nm, 21.3 nm, and 10.6 nm, for IWI, US-WI, and PSG catalysts, respectively. Study of the temperature effecton the MDR system showed that higher temperatures favored the MDR reaction with the side reaction playing vital roles. The catalyst synthesized by the PSG method showd higher carbon gasification rate with the stability up to 24 h, whereas catalysts from other synthesis methods were only active for less than 2 h, which could be due to the formation of higher amount of filamentous carbon, balance in oxygen species, and the smaller crystallite size of the PSG-20 wt% Ni/Pr2O3. The PSG-20 wt% Ni/Pr2O3 catalyst accumulated more filamentous carbon than graphitic carbon. In contrast, the IWI and US-WI catalysts accumulated mainly graphitic carbon which encapsulated the Ni0 sites, resulting in excess carbon deposition and reactor clogging within 2 h on stream. [ABSTRACT FROM AUTHOR]

Branched polyolefins with controllable topology structures were generated from the chain-walking (co)polymerizations of ethylene, 1-pentene (1P) and 2-pentene (2P) using Brookhart-type a-diimine Ni(II)-based catalysts possessing different para-substituted groups, {[(4-R-2-Et-6-Me-C6H2N = C)2Nap]NiBr2, Nap: 1,8-naphthdiyl; R = CHMePh, Ni1; R = Ph, Ni2; R = H, Ni3}. The X-ray diffraction analysis demonstrated that the crystalline structure of Ni1' is in centrosymmetric dimer structure mode with the bimetallic Ni center connected by two bromide bridges. The para-sec-phenethyl moiety in the catalyst Ni1 obviously improved its catalytic performance and thermal stability in the ethylene polymerization. The Ni1/Et2AlCl system showed great catalytic activities (up to 7.73×106 g·mol−1·h−1) and achieved polyethylene (PE) with alkyl chains, including Me, Et, n-Pr, n-Bu, sec-Bu branches and longer chains (Lg). Compared with the 1-pentene polymerization, this catalyst system successfully mediated the polymerization of 2P to give highly branched polymers with approximately 195 branches/1000C possessing Me, Et, and n-Pr branches and a long methylene sequence due to the monomer isomerization. The Et branches derived from 2,3-insertion is slightly less than the sum of Me and n-Pr branches derived from 3,2-insertion, indicating that the 3,2-insertion mode is a slightly favorable pathway in the polymerization of 2P. [ABSTRACT FROM AUTHOR]

In this work, Ni/calcined Kieselguhr was promoted with Cu and Mg to enhance the hydrogenation of soybean oil. The experimental design software was used to study the impact of each metal on catalyst activity and find the best Ni–Cu–Mg composition. The prepared catalysts were characterized by BET, FESEM, EDX-elemental mapping and H2-TPR analyses. The catalytic activity of all prepared catalysts was examined in a semi-batch reactor. The best catalytic composition was obtained to be 0.604 Ni, 0.223 Cu, and 0.173 Mg values (based on the mass fraction of the prepared catalyst with the total activated catalyst weight of 21 wt%). The highest catalytic activity and fatty acid conversion, 77.6 IV and 69.0% linoleic acid conversion, were found at optimum conditions. Kinetic studies indicated that the reaction rate depends on catalyst composition. The optimum catalyst exhibited a significant rate constant for linolenic and linoleic acid conversion with the selectivity of 1.212 and 2.218. [ABSTRACT FROM AUTHOR]

Over the past few decades, carbon hybrid composites have attracted the attention of many researchers for their applications in catalytic processes and pollutant removal. Carbon fiber felt/carbon nanotube (CFF/CNT) hybrid composites are promising candidates for such applications due to their high specific surface area, chemical stability, and high adsorption capacity as a result of the CNTs present in their composition. In this study, CFF/CNT hybrid composites were fabricated by methane decomposition on nickel surface in a CVI process at 700 °C over different times. The produced catalyst was characterized in terms of its shape, size, and distribution of the catalytic nickel particles formed on the surface of the CFF. Then, the desired composites had been fabricated; SEM, FESEM, and TEM were employed to investigate the morphology and the growth mechanism of the CNT; FTIR-ATR and Raman were used to determine its chemical structure; XRD technique was exploited to identify the phase structure; and BET was employed to measure the specific surface area while their mechanical properties were also characterized. FESEM images of the composite specimens confirmed the presence of CNTs 38–56 nm in diameter on the surface of the fibers. It was also observed that, with increasing process duration, the nanotubes did not lose their nanometric structure and they grew slightly larger in diameter due to the formation of new walls. Their lengths also increased by up to several micrometers. This increase in length and the intertwining of the synthesized CNTs resulted in the formation of a complex 3D CNT network around the CFF fibers. The BET test results also indicated an increase in specific surface area from 36.29 m2/g to 53.80 m2/g due to the increase in CVI process time from 2 to 10 h. Meanwhile, flexural strength exhibited a significant increase from 0.58 MPa (for CFF) to 1.36 MPa after 10 h of CVI. Finally, TEM images revealed CNT nucleation and growth in a bamboo- and octopus-like growth mechanism. [ABSTRACT FROM AUTHOR]

Ni-based catalysts supported on CeO2 doped with Gd were prepared in this work to investigate the role of gadolinium on ethanol conversion, H2 selectivity, and carbon formation on ethanol steam reforming reaction. For this, catalysts containing 5 wt% of Ni impregnated on supports of ceria modified with different amounts of Gd (1, 5, and 10 wt%) were used. Ex-situ studies of XRPD suggest an increase of the lattice parameters, indicating a solid solution formation between Gd and Ce. Results of TPR showed an increase in metal-support interactions as the content of Gd increased. In situ XRPD studies indicated the formation of a GdNiO ternary phase for the catalysts containing Gd, which is in agreement with the results obtained by XANES. The catalysts were tested at three temperatures: 400 °C, 500 °C, and 600 °C. The conversion and productivity showed dependence with the Gd content and also with the temperature of the reaction. After the catalytic tests, catalysts containing Gd presented filamentous carbon possible due to a change in the reaction pathway. The highest ethanol conversion and H2 productivity were obtained at 600 °C for all catalysts and the best catalyst at this temperature was 5Ni_5GdCeO2. The promising performance of this catalyst may be associate with the lowest formation of GdNiO ternary phase, among the catalysts containing Gd, which means more Ni0 active species available to convert ethanol. [ABSTRACT FROM AUTHOR]

In this paper, the acceleration effect of nickel (Ni) on the direct nitridation process of the diamond-wire saw powder (DWSP) was investigated. The DWSP doped with Ni additives were nitrided at different temperatures. To study the mechanism of accelerated nitridation, the thermodynamics of Si-O-N-Ni and nitridation processes were analyzed by FactSage 7.2 and single-crystal silicon blocks were also nitrided instead of the DWSP. The results revealed that Ni decreased the nitridation temperature at which the DWSP began to gain significant weight and exhibited an excellent accelerating effect on the nitridation of the DWSP. At 1300°C the DWSP containing 2.0 wt% Ni additives had been completely nitrided within 2 h, whereas the DWSP without Ni additives had not been nitrided yet. Based on the equivalent substitution experiment, it could be concluded that the presence of Ni additives accelerated the nitridation and promoted the formation of the α-Si3N4 nanorods through facilitating the generation of the SiO(g) and destructing the silica film on the surface of silicon at lower temperature. Meanwhile, Ni additives also played an important part in the growth of α-Si3N4 nanorods by forming liquid Ni-Si alloy in the product. [ABSTRACT FROM AUTHOR]

The α-imino-ketone nickel catalyst is an emerging versatile platform that is easy to prepare and allows for the production of branched high molecular weight functionalized polyethylenes. However, study on this catalyst system is rare thus far. In this contribution, by introducing different backbones, flexible and rigid axial substituents into the α-imino-ketone framework, a family of cationic nickel catalysts were synthesized and fully characterized. Without the addition of any activator, systematic studies on ethylene polymerization and copolymerization with polar monomers were performed to explore the influence of both backbone and axial substituent on catalytic activity, polymer molecular weight, branching density and incorporation. In particular, owing to the unique semi-opening feature of the α-imino-ketone framework, the preferred nickel catalyst exhibited high activity of 175 kg·mol−1·h−1 to produce functionalized polyethylene with molecular weight of 13.4 kg·mol−1 and comonomer incorporation of 2.9 mol%. [ABSTRACT FROM AUTHOR]

Ni nanoparticle catalysts embedded in ZrO2 porous spheres and ZrO2 porous composite spheres, SiO2-ZrO2, MgO-ZrO2, and Y2O3-ZrO2, with 83−115 nm diameter and 167–269 m2/g specific surface area were prepared by a one-pot and one-step solvothermal reaction from precursor solutions consisting of Ni(NO3)2‧6H2O, Zr(OnBu)4, and acetylacetone in moist ethanol combined with either Si(OEt)4, magnesium acetylacetate, or Y(OiPr)3. The obtained Ni catalysts have high specific surface areas of 130–196 m2/g, even after high-temperature reduction by H2 at 450 °C for 2 h. They were utilized as catalysts for low-temperature dry reforming of methane (DRM) at 550 °C to suppress carbon deposition on Ni nanoparticles. The Ni catalysts embedded in SiO2-ZrO2 and Y2O3-ZrO2 demonstrated high catalytic activity and long stability in the reaction. Moreover, carbon deposition on Ni nanoparticles in the DRM reaction was effectively suppressed in when using the SiO2-ZrO2 and Y2O3-ZrO2 composites. [ABSTRACT FROM AUTHOR]

This article considers the catalytic and physicochemical properties of composite materials obtained by the heat treatment of nickel nitrate immobilized on polyvinyl alcohol (PVA). The effects of the composite formation temperature on the phase composition of the metal-containing particles and their size were studied. The composite material obtained was found to be an active catalyst for the hydrogenation of carbon monoxide without a pre-activation step. The following synthesis parameters were achieved: 29% carbon monoxide conversion under conditions for catalytic hydrogenation and 28 g/m3 methane yield. Hypotheses were offered concerning the effect of particle size on the activity of the synthesized composite and an effect of the volume velocity on the carbon monoxide hydrogenation process parameters was demonstrated. [ABSTRACT FROM AUTHOR]

As phosphines readily invert, the synthesis of P-chiral phosphines is a challenging task and has been rarely investigated. We report the synthesis of a nickel complex [Ni-((S,S)Me-FerroLANE)(phenyl)(I)] (Ni-Cat.1) and its performance in a P-C coupling reaction to generate P-chiral phosphine. The Ni-Cat.1 was synthesized by mixing ligand (S,S) Me-FerroLANE with the metal precursor [(diphenylphosphanyl)nickel(phenyl)(I)] in good yield. Ni-Cat.1 was characterized using different spectroscopic and analytical techniques. Treatment of racemic methyl(phenyl)phosphine (1) with 1-(3-iodophenyl)urea (2) produced the corresponding P-chiral supramolecular phosphine (3). Optimization of reaction parameters produced sulfur protected phosphine N-(3-(methyl(phenyl)phosphorothioyl)phenyl)formamide (3’) with excellent enantiomeric excess (99% ee) and moderate conversion (51%). [ABSTRACT FROM AUTHOR]

For the rational design of metal catalyst in olefin polymerization catalysis, various strategies were applied to suppress the chain transfer by bulking up the axial positions of the metal center, among which the "sandwich" type turned out to be an efficient category in achieving high molecular weight polyolefin. In the α-diimine system, the "sandwich" type catalysts were built using the typical 8-aryl-naphthyl framework. In this contribution, by introducing the rotationally restrained benzosuberyl substituent into the ortho-position of N-aryl rings, a new class of "sandwich-like" α-diimine nickel catalysts was constructed and fully identified. The rotationally restrained benzosuberyl substituents played a "sandwich-like" function by capping the nickel center from two axial sites. Compared to the nickel catalyst Ni1 bearing freely rotated benzhydryl substituent, Ni2 featuring benzosuberyl substituent enabled the increase (8 times) of polymer molecular weights from 8 kDa to 65 kDa in the polymerization of ethylene. By further increasing the steric bulk of another ortho-site of the N-aryl ring, the polymer molecular weight even reached an ultrahigh level of 833 kDa (Mw=1857 kDa) using the optimized Ni3. Notably, these nickel catalysts could also mediate the copolymerization of ethylene with methyl 10-undecenoate, with Ni3 giving the highest copolymer molecular weight (88 kDa) and the highest incorporation of comonmer (2.0 mol%), along with high activity of up to 105 g·mol−1·h−1. [ABSTRACT FROM AUTHOR]

3-iodopropionic acid (3-IPA) can be efficiently synthesized from the glycerol derivative glyceric acid (GA), which is a potential biomaterial-based platform molecule. In this report, ethyl 3-iodopropionate was rapidly dimerized to diethyl adipate in a microwave reactor using NiCl2·6H2O as a catalyst, co-catalyzed by Mn and the 1, 10-Phenanthroline monohydrate ligand. Under the optimum reaction conditions, diethyl adipate can be obtained with 84% yield at 90 °C in just 5 min. Diethyl adipate was hydrolyzed to obtain the adipic acid (AA) in 89% yield with an acid catalyst. AA is an important chemical and a monomer for producing a wide range of high-performance polymeric substances. This rapid coupling method is also applicable to other alkyl halides. [ABSTRACT FROM AUTHOR]

The physicochemical and catalytic properties of 6%Ni/Al2O3 catalysts in the gas-phase hydrodechlorination of chlorobenzene (CB) are studied. The catalysts are synthesized by supporting nickel nitrate on two types of alumina—A (synthesized by aluminum isopropoxide hydrolysis) and E (manufactured by Engelhard)—with different morphologies and textures; some of the samples are unmodified, and some are modified by depositing 20% heteropoly acid (HPA) H8Si(W2O7)6 ⋅ nH2O. To prevent the HPA from decomposition, the air calcining and reduction of the modified materials are conducted at relatively low temperatures (250 and 330°C, respectively). To provide an adequate comparison, the catalysts containing no HPA are subjected to a similar treatment. Temperature-programmed reduction (TPR) reveals that air calcining at 250°C does not provide the complete conversion of the original nickel nitrate to oxide; nickel nitrates and hydroxynitrates are present in the catalyst precursors; their content decreases upon modification with the HPA. Differences in the composition and strength of Lewis acid sites on the surface of two types of Al2O3 lead to dissimilar coordination of nitrate and differences in nickel reducibility, as revealed by TPR, diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy with CO adsorption, and in situ X-ray photoelectron spectroscopy (XPS). Nickel contained in Ni/Al2O3(E) undergoes reduction somewhat more readily than nickel in Ni/Al2O3(A) does; however, the conditions used in this study provide the reduction of only a small portion of nickel in the two catalysts. According to in situ XPS, TPR, and DRIFT spectroscopy with CO adsorption, the modification of Ni/Al2O3 with the HPA leads to a further change in the acidic properties and the coordination of nickel nitrate during impregnation and an increase in nickel reducibility; it prevents nickel from migration from the surface into the bulk of the sample and leads to the formation of new active sites owing to the strong nickel–tungsten interaction in the HPA. Depending on the nature of the support, modification with the HPA leads to an improvement (Ni/HPA/Al2O3(A)) or deterioration (Ni/HPA/Al2O3(E)) of the catalytic efficiency of the samples. At high temperatures, the benzene selectivity of the HPA-modified catalysts decreases owing to the formation of cyclohexane. The catalyst efficiency increases in the following order: Ni/HPA/Al2O3(E) < Ni/Al2O3(A) < Ni/Al2O3(E) < Ni/HPA/Al2O3(A). The most active catalyst—Ni/HPA/Al2O3(A)—exhibits the highest stability in long-term tests with an increase and subsequent decrease in temperature. The effect of nickel reducibility on the catalyst efficiency in CB hydrodechlorination is more significant than the effect of differences in texture and nickel content. [ABSTRACT FROM AUTHOR]

The low oxidative stability of first generation biodiesel is one of the most important challenges to be overcome in biodiesel technology. A nickel/bentonite catalyst was prepared and applied in partial hydrogenation of Jatropha oil biodiesel for improving the oxidative stability of biodiesel. The catalyst was characterized by N2 adsorption–desorption, inductively coupled plasma-atomic emission spectrometer (ICP-AES), thermogravimetry-differential scanning calorimetry (TG-DSC), and transmission electron microscope (TEM). The main reaction parameters of partial hydrogenation such as reaction temperature, catalyst dosage, reaction pressure, stirring rate and reaction time were optimized. The mass conversion ratio of C18:2 up to 75% at the optimized hydrogenation conditions, and for the hydrogenated biodiesel, the contents of C18:2, c-C18:1, t-C18:1 and C18:0 were 7.64, 42.7, 24.06 and 14.67 wt%, respectively. After partial hydrogenation, the oxidative stability of hydrogenated biodiesel significantly increased from 6.5 h of feed Jatropha oil biodiesel to 18.0 h. The nickel/bentonite catalyst was recovered and reused for five consecutive cycles without any significant loss of the catalytic activity. Overall, via partial hydrogenation, the oxidative stability of biodiesel could be significantly provided using this effective nickel/bentonite catalyst. A bentonite-based nickel catalyst was prepared and used in partial hydrogenation of Jatropha oil biodiesel [ABSTRACT FROM AUTHOR]

Furfural is a key bioderived platform molecule, and its hydrogenation affords access to a number of important chemical intermediates that can act as "drop-in" replacements to those derived from crude oil or novel alternatives with desirable properties. Here, the vapour phase hydrogenation of furfural to furfuryl alcohol at 180 °C over standard impregnated nickel catalysts is reported and contrasted with the same reaction over copper chromite. Whilst the selectivity to furfuryl alcohol of the unmodified nickel catalysts is much lower than for copper chromite as expected, the activity of the nickel catalysts in the vapour phase is significantly higher, and the deactivation profile remarkably similar. In the case of the supported nickel catalysts, possible contribution to the deactivation by acidic sites on the catalyst support is discounted based on the similarity of deactivation kinetics on Ni/SiO2 with those seen for less acidic Ni/TiO2 and Ni/CeO2. Powder X-ray diffraction is used to exclude sintering as a primary deactivation pathway. Significant coking of the catalyst (~ 30 wt% over 16 h) is observed using temperature programmed oxidation. This, in combination with the solvent extraction analysis and infrared spectroscopy of the coked catalysts points to deactivation by polymeric condensation products of (reactant or) products and hydrocarbon like coke. These findings pave the way for targeted modification of nickel catalysts to use for this important biofeedstock-to-chemicals transformation. [ABSTRACT FROM AUTHOR]

In this work, NiO supported mesostructured silica nanoparticles (MSN) were synthesized via the urea–nitrate combustion method using urea as fuel and nitrate salts as oxidants with the different urea/nitrate ratios and calcination duration. The physicochemical properties of catalysts were investigated by several techniques, including N2 physisorption measurements, powder X-ray diffraction, N2-BET isothermal adsorption, hydrogen temperature-programmed reduction, carbon dioxide temperature-programmed desorption, scanning electron microscopy and transmission electron microscopy. The obtained catalysts were employed in the methanation of CO2-rich gas at a temperature range of 225–400 °C with the CO2/H2 ratio of 1/4 and CO2 concentration of 20 mol%. The results showed that using the urea–nitrate combustion method in synthesizing catalysts led to improved physicochemical properties that increased the activity of NiO/MSN catalysts. The catalyst prepared with the urea/nitrate molar ratio of 3 and calcined at 600 °C for 3 h showed the highest catalytic performance in methanation of CO2-rich gas, reaching CO2 conversion of 96% and CH4 selectivity of 100% at 375 °C. The best catalyst has excellent stability in CO2 solo-hydrogenation at a reaction temperature of 375 °C during 30 h of reaction thanks to the resistance to coke formation. Besides, adding 1 mol% CO in the feedstock should be simultaneously conducted to surge the effectivity of CO2 methanation. [ABSTRACT FROM AUTHOR]

A systematic study of the surface of Raney nickel-based pyrophoric catalysts by small-angle X-ray diffraction analysis was carried out for the first time. The parameters of the crystallites constituting the active catalyst surface were determined. A correlation between the surface structure and the activity of skeletal nickel for the liquid-phase hydrogenation reactions was demonstrated. The effect of treatment of Ni–Al alloy with sodium hydroxide and hydrogen peroxide on the catalyst particle size and on the course of the hydrogenation reaction was revealed and substantiated. The X-ray diffraction data on the catalyst surface structure and the adsorption calorimetry data were correlated with the skeletal nickel activity parameters. [ABSTRACT FROM AUTHOR]

A thermodynamic analysis is performed of the patterns of steam conversion of natural gas at temperatures of 300–600°C, pressures of 0.1–4 MPa and H2O : C molar ratios of 0.8‒1.2. Under these conditions, the reaction product is methane–hydrogen mixtures with hydrogen concentrations of 10–30 vol %. A rise in temperature, molar ratio Н2О : С, and a decrease in pressure contribute to an increase in the concentration of hydrogen in the reaction products. The thermodynamic boundaries of the process with no carbonization of the catalyst are determined. Experiments are performed to obtain methane–hydrogen mixtures from methane with an output concentration of 15–35 vol % hydrogen on industrial Ni-CrOx-Al2O3 catalyst at 325–425°C, a H2O : C molar ratio of 0.8–1.0, and atmospheric pressure. It is shown that under these conditions, the process proceeds without the formation of carbon on the catalyst. [ABSTRACT FROM AUTHOR]

An approach to C–N cross-coupling reactions of aryl halides with amines in the presence of an amide-based pincer nickel(II) catalyst (2) is described. For 3 h reactions at 110 °C with 0.2 mol% catalyst, aryl bromides gave higher turnover numbers (TON) than the corresponding chlorides or iodides. Both primary and secondary amines could be used with the former giving higher TON. However, sterically hindered amines showed lower TON. In elucidating the mechanism of this nickel complex-catalyzed C–N cross coupling reaction it was found that the rate of reaction was unchanged in the presence of radical quenchers and a plausible Ni(I)–Ni(III) pathway is proposed. Nickel pincer catalyst proved to be excellent catalyst for the C-N cross-coupling reaction with the high turnover number (TON) for 1° and 2° amines and different nonactivated aryl halides under optimum conditions. [ABSTRACT FROM AUTHOR]

Mechanical milling and a gas-selective polymer were used to protect MgH2 from oxidation and improve its dehydrogenation properties. MgH2 and poly(methyl methacrylate) (PMMA) were simultaneously ball-milled for 5 and 20 h, respectively, to prepare an air-resistant nanostructured composite. The properties of the nanostructured composite were studied by XRD, SEM, and FTIR methods. The dehydrogenation performance of all samples was investigated by TGA analysis. The hydrogen desorption performance of ball-milled samples was also evaluated after exposure to air for 4 weeks. Results showed that MgH2 desorbed about 0.79 wt.% of hydrogen after heating up to 300 ˚C and holding for 15 min at this temperature. The ball-milling of MgH2 and PMMA for 5 and 20 h led to hydrogen desorption of 6.21 and 6.10 wt.% after heating up to 300 ˚C and holding for 15 min at this temperature, respectively, which proved the surface protection of MgH2 from oxidation by PMMA. After 4 weeks of exposing the ball-milled MgH2–PMMA samples to air, their hydrogen desorption percentage at the same condition changed to 5.80 and 5.72 wt.% for 5 and 20 h milled samples, respectively. A slight reduction in the dehydrogenation percentage of air-exposed samples proved that the air stability of MgH2 had been significantly enhanced by its confinement with PMMA. [ABSTRACT FROM AUTHOR]

The two-stage conversion of industrial liquefied hydrocarbon gases (LHGs) on NIAP-07-01 (NKM-1) and NIAP-03-01 catalysts is studied to obtain hydrogen-containing gases. The experiments are performed in flow reactors with fixed catalyst layers at a pressure of 0.1 MPa under the conditions of pre-reforming: temperature, 350–450°С; GHSV = 1000–3000 h−1; steam : gas ratio, (4 : 1)–(8 : 1). For steam–air reforming: temperature, 700°С; GHSV = 2000 h–1; air : gas ratio, 1.2 : 1. The concentrations of converted gas components under these conditions correspond to equilibrium values calculated using the Peng–Robinson model. The conversion of methane homologs is almost 100% during the pre-reforming stage, while the concentrations of methane and hydrogen are 32–54 and 24–47%, respectively. The main condition for the pre-reforming of hydrocarbon gases with a high methane equivalent is a Н2О : С ratio greater than 2 to avoid the formation of elemental carbon (carbonization). The yield of hydrogen-containing gas during two-stage reforming is 15.6 m3, obtained from 1 m3 of initial LHGs with a hydrogen content of 41.81%, and the total amount of CO and H2 is more than 52%. [ABSTRACT FROM AUTHOR]

This work investigates the process of elimination of carbon deposits formed during the mixed reforming of methane mixture. The mixed reforming of methane to synthesis gas was studied over Ni/Al2O3 catalyst in the 650–750°C. The amount of carbon deposit on the surface of catalyst varied from 2.8 to 5.9%, depending on the reaction temperature. The reactivity of carbon species was evaluated in the oxygen, hydrogen, carbon dioxide, and water mixtures. The obtained results revealed the presence of highly active carbon form (etched at a temperature below 200 °C) and inactive form (gasification at a temperature above 500 °C). The SEM and Raman analyses confirmed the presence of carbon in the form of filaments. Among all investigated gasification agents, water vapor was found to be the most efficient in removing the carbon deposit due to better adsorption of water on the surface of aluminum oxide. The overall mechanism of mixed methane reforming along with carbon gasification was shown. [ABSTRACT FROM AUTHOR]

Electrocatalytic glucose oxidation is a very important reaction in glucose fuel cell and medical diagnosis, which is limited by sluggish reaction kinetics and low diffusion coefficient. Herein, a composite (donated as Ni6/AB) consisting of atomically precise nickel catalyst with defined crystal structure [Ni6(SC12H25)12] and acetylene black(AB) has been initiated as a novel and high-efficient non-noble metal catalyst for the electrochemical oxidation of glucose benefiting from its high exposure of active sites and increased electron/mass transport. The present Ni6/AB composites display the onset potential of +1.24 V and the maximum current density of 5 mA cm−2 at the potential of +1.47 V in the electrolyte of 0.1 M KOH with 5 mM glucose. This electrochemical performance is much superior to the alone nickel catalysts, acetylene black, and previous reported nanomaterials. Furthermore, the obtained Ni6/AB composites are also expected to find important application in the electrochemical detection of glucose due to its high electrochemical performance. The sensitivity and the detection of limit are determined to be 0.7709 mA cm−2 mM−1 and 1.9 μM, respectively. Our study demonstrates that atomically precise nickel catalysts on acetylene black could be potential promising materials for next-generation energy devices and electrochemical sensors. [ABSTRACT FROM AUTHOR]

A series of C7-substituted-2-morpholino-N-(pyridin-2-ylmethyl)quinazolin-4-amine derivatives 3a–3t were synthesized by using Nickel catalyzed Kumada cross coupling reaction. The structure of the key intermediate 2 was assigned using 2D COSY and 2D NOESY correlation spectrum. All the target compounds were characterized and tested for their antibacterial activity against Gram-positive organisms such as Bacillus subtilis, Staphylococcus aureus, Staphylococcus epidermidis, and Gram-negative organisms such as Escherichia coli, Pseudomonas aeruginosa, and Klebsiella pneumonia. The results indicated that compounds 3g–3m exhibited potent antibacterial activity with MIC values ranging from 1.17 to 4.68 μg/mL. These results are expected to be of help in understanding the structure activity relationship and further enable us to design novel antibacterial agents. Molecular docking of Escherichia coli Biotin Carboxylase (EcBC) enzyme was also performed in order to study the interactions of the synthesized compounds. [ABSTRACT FROM AUTHOR]

Nanocrystalline Ni/Al2O3 catalysts and promoted Ni-M/Al2O3 (M = Ce, La, Mg, K) catalysts were employed a in reverse water gas shift reaction. Among the prepared nickel catalysts 5% Ni/Al2O3 catalyst showed high CO2 conversion and CO selectivity. To improve the CO2 conversion and CO selectivity of 5% Ni/Al2O3, 1 or 2 wt% Ce, La, Mg or K were used. One percent La and 2% K showed highest CO2 conversion and CO selectivity. The high activity and CO selectivity of promoted catalysts can be accredited to the increase of Ni dispersion (or smaller Ni particles), concentration of surface active sites and CO2 adsorption by basic nature of promoters. The prepared samples were characterized by X-ray diffraction, inductively coupled plasma emission spectroscopy, N2 adsorption–desorption (BET), temperature programmed reduction (TPR), scanning electron microscopy and transmission electron microscopy (TEM) techniques. The BET surface area of prepared γ-alumina support was 126.81 m2 g−1, impregnation of the support with Ni and promotion of 5 wt% Ni with K and La reduced the specific surface area. The support and catalysts possessed mesoporous structure. The TPR-H2 analysis revealed higher Ni dispersion and reducibility for promoted nickel catalysts; 5Ni–2K showed highest reducibility. TEM images of 5Ni and 5Ni–2K showed increase of Ni dispersion and decrease of Ni particle size for the promoted catalyst. After 50 h on stream at 600 °C, 5Ni–1La and 5Ni–2K performed great catalytic stability. [ABSTRACT FROM AUTHOR]

Polymerizations of linear α-olefins (CnH2n, CH2 = CH―R, R = Cn−2) catalyzed by early transition metals typically afford amorphous polymers with alkyl chains (Cn−2), while chain-straightening polymerizations of α-olefins with nickel-based catalysts produce semicrystalline polyolefins. Polymerizations of various α-olefins were carried out using an α-diamine nickel catalyst with a significantly distorted chelating ring. The influences of temperature, monomer concentration, and chain length of α-olefins on polyolefin microstructure were examined in detail. The α-diamine nickel catalyst realized highly regioselective 2,1-insertion of α-olefins regardless of reaction temperature and monomer concentration. Increased chain length of α-olefins led to the formation of more linear polyolefin. Semicrystalline polyolefins with high melting temperatures (Tm) were made from α-olefins through highly regioselective 2,1-insertion and precise chain-straightening. [ABSTRACT FROM AUTHOR]

Nickel (oxy)hydroxides (NiOxHy) are promising cost-effective materials that exhibit a fair catalytic activity for the ethanol oxidation reaction (EOR) and could be used for sustainable energy conversion. Doping the NiOxHy structure with other metals could lead to enhanced catalytic properties but more research needs to be done to understand the role of the doping metal on the EOR. We prepared NiOxHy films doped with Fe or Co with different metallic ratios by electrodeposition and evaluated the EOR. We found a positive and negative effect on the catalytic activity after the incorporation of Co and Fe, respectively. Our results suggest that Ni atoms are the active sites for the EOR since Tafel slopes were similar on the binary and pristine nickel (oxy)hydroxides and that the formal potential of the Ni(II)/Ni(III) redox couple is a good descriptor for the EOR activity. This work also highlights the importance of controlled metal doping on catalysts and may help in the design and development of improved materials for the EOR. [ABSTRACT FROM AUTHOR]

A highly selective synthesis of acetonitrile was carried out by the reaction of ethanol with ammonia on a 10 wt% Ni/Al2O3 catalyst. The conversion of ethanol and selectivity to acetonitrile, ethylene, and monoethylamine were examined by varying experimental parameters such as ammonia partial pressure, reaction temperature, and space time. The increase in the ammonia partial pressure led to a considerable decrease in the conversion and small increase in the acetonitrile selectivity up to a molar ratio of NH3/ethanol of 3, followed by almost constant values. The partial reaction order of ethanol obtained by controlling the space time was one, while that of ammonia was negative, −0.4. The deactivation behavior of the catalyst after 100 h on stream reaction at 230 °C was analyzed by X-ray photoelectron spectroscopy and temperature programmed oxidation of the catalyst used. The catalyst deactivation was attributed to the gradual formation of nickel carbonitride on the catalyst surface. [ABSTRACT FROM AUTHOR]

A method for the determination of the total amounts and physical parameters of adsorbed individual hydrogen species on the surface and in the bulk of metal catalysts of liquid-phase hydrogenation reactions by simultaneous thermal analysis mass spectrometry was proposed. The adsorptions of reactive hydrogen on a skeletal nickel catalyst in an aqueous medium were estimated. The concentrations of metal-hydrogen complexes with different binding energies on the surface of the catalyst in the liquid phase were determined by a direct experimental method. [ABSTRACT FROM AUTHOR]

The performance of alumina supported unpromoted and cerium promoted nickel catalysts in CO2 methanation reaction was investigated. It was found that the activity of catalysts in CO2 methanation reaction at low reaction temperatures can be improved by the increase in nickel loading and introduction of cerium promoter. The catalysts showed high resistance for sintering and coking at high reaction temperatures. A few stages of catalysts deactivation by H2S in the methanation reaction carried out at 475 °C with the time on stream were identified. It was found that an introduction of H2S to the stream (8 ppm) did not induce rapid decrease of activity. Slight and then strong drop of CO2 conversion and simultaneously the loss of methane selectivity was observed after specific time, depending on the catalysts composition. Deactivation of catalysts was related to the nickel content and the presence of cerium. X-ray diffraction studies indicated small changes of crystallite size with the time on stream. Raman spectroscopy studies pointed out that deactivation of catalysts was not connected with formation of carbon deposits. An in-situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy studies showed that exposition of catalysts to the reaction mixture containing the traces of H2S led to the blocking of nickel active sites responsible for CO2 and H2 activation and successive transformation to carbonyl and formate species. [ABSTRACT FROM AUTHOR]

Acetone steam reforming was carried out over olivine supported cobalt and nickel catalysts for producing hydrogen in high selectivity. The wet impregnation process was used for the preparation of the catalyst. The chemical and physical properties of synthesized catalysts were determined by BET, H2-TPR, SEM (coupled with EDS) and XRD. The reforming activity was examined at atmospheric pressure in a tubular reactor. The olivine supported bimetallic (Ni–Co) catalysts exhibited significant acetone steam reforming activity with around 99% conversion of acetone. Around 80% selectivity to hydrogen was obtained over bimetallic 5% (Ni25Co75)/olivine. A LHHW type kinetic model was established for the reforming process consisting of complex reaction networks. The activation energy for the LHHW model was found to be 63 kJ/mol. [ABSTRACT FROM AUTHOR]

The formation of the C–C bond is a major and important reaction in synthetic organic chemistry and frequently catalyzed by transition-metal catalysts. Among them, Kumada–Tamao–Corriu coupling reaction is providing a simple methodology and extensively employed in the art of organic synthesis. In this review, we try to highlight the recent advances in the applications of Kumada–Tamao–Corriu coupling reaction by updating of our previous review from 2012 up to date. [ABSTRACT FROM AUTHOR]

Residual biomass shows potential to be used as a feedstock for fast pyrolysis bio-oil production for energetic and chemical use. Although environmentally advantageous, further catalytic upgrading is required in order to increase the bio-oil stability, by reducing reactive compounds, functional oxygen-containing groups and water content. However, bio-oils may separate in fractions either spontaneously after ageing or by fractionated condensation. Therefore the effects of upgrading on different fast pyrolysis bio-oil (FPBO) fractions obtained from a commercially available FPBO were studied by elemental analysis, GC-MS and 1H-NMR. Not only the FPBO was upgraded by catalytic hydrotreatment, but also the heavy phase fraction formed after intentional aging and phase separation. The reactions were conducted between 175 and 325 °C and 80-100 bar by using a nickel-chromium catalyst in batch experiments. The influence of the hydrotreatment conditions correlated with the composition of the upgraded products. Higher oxygen removal was obtained at higher temperatures, whereas higher pressures resulted in higher hydrogen consumption with no significant influence on deoxygenation. At 325 °C and 80 bar 42% of the oxygen content was removed from the FPBO. Compounds attributed to pyrolysis oil instability, such as ketones and furfural were completely converted while the number of alcohols detected in the upgraded products increased. Coke formation was observed after all reactions, especially for the reaction with the fraction rich in lignin derivatives, likely formed by polymerization of phenolic compounds mainly concentrated in this phase. Independently of the feedstock used, the upgraded bio-oils were very similar in composition, with reduced oxygen and water content, higher energy density and higher carbon content. [ABSTRACT FROM AUTHOR]

In this research, the effect of Ce, Cu and Ce-Cu promoters on the performance of Ni/SBA-16 catalyst in partial oxidation of methane reaction was investigated. The Ni/SBA-16 catalyst with 9.1 wt% Ni content without promoter and Ni/SBA-16 catalyst promoted with cerium, copper, copper-cerium with equimolar to nickel content were prepared and their performance in methane partial oxidation reaction were evaluated. The prepared catalysts were characterized by XRD, N2 adsorption and EDX-FESEM analysis techniques. The N2 adsorption isotherms of catalyst samples showed that adding promoters to the Ni/SBA-16 catalyst partly decreased the surface area of catalysts. Furthermore, the results using XRD analysis partly demonstrated dispersion of nickel particle for catalyst Cu-promoted. Also, SEM analysis showed a similar size of nano crystallites in the range of 8-20 nm for all catalyst samples. The results of evaluation of catalytic activities of the catalysts showed high activity of unpromoted and Ce-promoted nickel catalyst in methane conversion (≈ 93%) remained stable for 3 h. The effects of other reaction parameters such as temperature, gas hourly space velocity and molar ratio of the feed were also evaluated and reported. [ABSTRACT FROM AUTHOR]

A series of Ni-based SBA-15 catalysts were prepared via a wet impregnation method and tested for hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL). A GVL yield of 56% was obtained over Ni-SBA-15 catalyst and the GVL yield increased to 64% as the addition of Fe. Compared with the results above, a better performance with 93% GVL yield was obtained over the Ni-Fe-Cu/SBA-15. Extensive catalysts characterization techniques including TPR, XRD, XPS and porosity analysis have been performed to study the nature of nickel-based catalysts. Porosity analysis and XRD showed that all the studied catalysts had a typical mesoporous texture. The TPR and XPS results indicated that there was a strong interaction among Ni, Fe and Cu species and the nickel species was relatively enriched on the surface of the catalysts, which could be accounting for the highest catalytic performance of the Ni-Fe-Cu-SBA-15 catalyst with GVL yield of 93%. In addition, the reaction parameters such as temperature, time, catalysts loading and H2 pressure have been systematically optimized, giving a near quantitative yield of GVL over Ni-Fe-Cu/SBA-15 in the presence of the reaction temperature of 200 °C, time of 5 h, mass ratio of catalyst/reactant LA 0.3 and H2 pressure of 3.0 MPa. [ABSTRACT FROM AUTHOR]

Global warming, fossil fuel depletion and fuel price increases have motivated scientists to search for methods for the storage and reduction of the amount of greenhouse gases, especially CO. The hydrogenation process has been introduced as an emerging method of CO capture and convertion into value-added products. In this study, new types of catalysts are introduced for CO hydrogenation and are compared based on catalytic activity and product selectivity. The physical properties of the samples are specified using BET. Iron catalysts supported on γ-AlO with different metal promoters ( X = Ni, K, Mn, Cu) are prepared through the impregnation method. Moreover, Fe-Ni catalysts supported on HZSM5-AlO and Ce-AlO are synthesized. Samples are reduced by pure H and involved in hydrogenation reaction in a fixed bed reactor (H/CO = 3, total pressure = 10 MPa, temperature = 523 K, GHSV = 2000, 1250 nml/min). All catalysts provide high conversion in hydrogenation reactions and the results illustrate that the selectivity of light hydrocarbons is higher than that of methane and CO. It is found that Ni has a promoting effect on the conversion fluctuations throughout the reaction with 66.13% conversion. Using combined supported catalysts leads to enhancing catalytic performance. When Fe-Ni/γ-AlO-HZSM5 is utilized, CO conversion is 81.66% and the stability of the Fe-Ni catalyst supported on AlO and Ce-AlO furthey improves. [ABSTRACT FROM AUTHOR]

The performance of synthesized nickel catalysts was evaluated in medium-temperature shift reaction (MTS, 320-360 °C). The catalysts were characterized by X-ray diffraction, scanning electron microscopy, temperature-programmed reduction, and CO temperature-programmed desorption. Reactor test of 10 wt%Ni/CeO showed high CO conversion (91%), but with high CH selectivity (90%). Therefore, 10Ni- xK/CeO ( x = 4, 6, 8, and 10 wt%) catalysts were synthesized via impregnation method to suppress the methanation reaction. Simultaneous impregnation of Ni and potassium led to better performance than sequential impregnation. Potassium, by increasing the hydroxyl group, led to decreased CH selectivity from 90 to 3% at 360 °C, and the 10Ni-6K/CeO catalyst exhibited the best activity, selectivity, and stability in severe conditions. Additionally, gas hourly space velocity of 12,000 h and steam-to-carbon ratio of 3 were selected as optimal operating conditions. To determine the effect of Mn addition to the support, reactor test of 10Ni-6K/CeMnO was also carried out, showing that the catalytic activity was less than for the ceria-supported sample at low temperatures, but due to the appropriate interaction of Mn with Ni, preventing catalyst sintering, the stability of the catalyst at high temperatures was improved and the Mn-containing catalyst showed higher CO conversion. [ABSTRACT FROM AUTHOR]

A fluorinated LTM catalyst of [bis( N, N′-2-fluorophenylimino)acenaphthene] nickel(ΙΙ) dibromide was prepared and applied for ethylene polymerization. We established a reasonable hypothesis, highlighting the role of fluorine in ligand structure. In addition, density functional theory (DFT) studies have been applied to strengthen our propositions. DFT calculations of the β-agostic cationic species at room temperature and 75 °C suggest that the β-agostic structure for the latter was destabilized by 19 eV which rendered it less prone to β-H transfer reactions than the species at room temperature. In addition, a mechanism for the catalyst deactivation for fluorinated α-diimine nickel based catalysts has been proposed. [ABSTRACT FROM AUTHOR]

Activity control for CO dissociation over supported Ni catalysts is very important for steam reforming, CO reforming, methanation, carbon formation, and other processes. In this work, a series of Ni/SiO catalysts were designed through thermal decomposition or dielectric barrier discharge (DBD) plasma decomposition. After a high temperature reduction, the main difference between the two catalysts was the structure of Ni nanoparticles, instead of the particles size. The plasma decomposed catalyst possesses smooth surface on Ni nanoparticles with less defect sites, leading to the activity control of CO dissociation. DBD plasma decomposed Ni/SiO catalysts have a low activity for CO dissociation with a low final carbon yield. The as-produced carbon materials over thermally decomposed or plasma decomposed are in the form of carbon onion particles or carbon nanotubes, separately. The growth mechanism of these two different carbon materials was also discussed. [ABSTRACT FROM AUTHOR]

This work aimed at the determination of the influence of various types of lignocellulosic biomass on the performance of Ni/ZrO catalyst modified by CaO in the production of hydrogen rich gas from lignocellulosic feedstock. The catalysts were prepared by co-impregnation and sequential impregnation methods. The catalytic activity of the synthesized materials was examined in the high temperature conversion of cellulose (model compound) and real biomass samples-woodchips from pine, beech, birch and poplar. The surface properties of Ni/CaO-ZrO catalysts were characterized by X-ray diffraction (XRD), time-of-flight secondary ion mass spectrometry (ToF-SIMS), thermogravimetric analysis (TG-DTA-MS) and BET methods. The obtained results revealed that an incorporation of calcium into the structure of the catalyst led to a decrease in the coke formation rate on its surface. Moreover, the influence of the preparation method on the material composition and related properties was demonstrated. [ABSTRACT FROM AUTHOR]

The relationship between the properties with the composition of nickel-aluminium mixed oxides was investigated in this work. Ni-Al materials with Ni/Al molar ratios between 0.5 and 9 were synthesised via co-precipitation. The samples were characterised using the following techniques: surface area measurements ( S ), thermogravimetry, X-ray diffraction and temperature-programmed reduction, desorption and oxidation (H-TPR, NH-TPD and TPO/DTA). Samples with Ni/Al ratio = 0.5 primarily formed the AlO phase, whereas Ni/Al ratio = 9 mainly led to the bulk NiO phase. However, Ni/Al ratios between 1 and 3 favoured the formation of the mixed oxide phase with increased thermal stability and specific surface area and decreased crystallite sizes. The lower Ni/Al ratios led to the production of ethylene, which is likely related to the higher number of sites with stronger acidity. The samples with Ni/Al ratios of 2 and 3 promoted selectivity towards synthesis gas. For higher Ni/Al ratios, low thermal stability leading to sintering and deactivation due to coke formation was observed. [ABSTRACT FROM AUTHOR]

Systematic studies were performed on low-temperature steam conversion or low-temperature steam reforming (LTSR) of propane in an excess of methane on a Ni-based catalyst. The LTSR of the methane-propane mixture is a two-stage process involving the irreversible steam conversion of propane into carbon dioxide and hydrogen and reversible methanation of carbon dioxide. Above ~250°C, the methanation of carbon dioxide is quasi-equilibrium. The rate of propane conversion during the LTSR of the methane-propane mixture is first-order based on propane; its activation energy is ~120 kJ/mol and is almost independent of the methane, carbon dioxide, hydrogen, and steam concentrations. This very simple macrokinetic scheme allows us to correctly describe the experimental data and predict the temperature and flow rate of the mixture at which complete conversion of propane is achieved. [ABSTRACT FROM AUTHOR]

Various core-shell structured Ni@SiO nanocatalysts were prepared to provide an insight into the intrinsic effects of shell structures on the ammonia decomposition activity. The thickness of silica shell structure can be fine tuned in the range of 5-20 nm. With the increase in shell thickness, it was found that the catalytic activity did not decrease obviously, even though the reducibility determined by H-TPR exhibited a noticeable changes. As for the porosity of the shell, the SP-1 sample with a well-developed pore structure showed better catalytic performance than the SP-0 sample with a less-developed pore structure. It can be concluded that diffusion limitations would be greatly influenced by shell porosity nor shell thickness to some extent. Graphical Abstract: Various core-shell structured Ni@SiO nanocatalysts were prepared to provide an insight into the intrinsic effects of shell structures on the ammonia decomposition activity. The thickness and porosity of silica shell structure were fine tuned. It was concluded that diffusion limitations would be probably greatly influenced by shell porosity nor shell thickness to some extent. [ABSTRACT FROM AUTHOR]

Mesoporous nanocrystalline nickel-alumina promoted catalysts with high surface area were prepared by microemulsion (ME) method and employed in dry reforming of methane reaction. The catalysts were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller surface area analysis (BET), temperature programmed reduction (TPR) and temperature programmed oxidation (TPO) techniques. The results showed that the prepared catalysts had high porosity with great surface area and small crystallite size. Among the KO, MgO, CaO and BaO promoters, the MgO promoter showed considerable effect on catalytic performance and coke suppression of catalyst. [ABSTRACT FROM AUTHOR]