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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]

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]

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]

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]

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]

MgO nanosheets possessing the (111) facet as the main surface were synthesized and the Ni catalyst supported on MgO(111) nanosheets was investigated for the carbon dioxide reforming of methane. The catalytic activity and carbon deposition were compared between Ni/MgO(111) and Ni/MgO(commercial) catalysts. The results showed that Ni/MgO(111) performed at a higher activity as well as a longer stability. From the characterization results, the improved catalytic performances of Ni/MgO(111) were suggested to be closely associated with both the high dispersion of active Ni particles owing to the strong metal-support interaction and the large amount of basic sites of MgO(111) due to its unusual surface properties. [ABSTRACT FROM AUTHOR]

The kinetics of methane steam reforming were studied on a Ni/Mg/K/AlO catalyst that was developed for conditioning of biomass-derived syngas. Reactions were conducted in a packed-bed reactor while the concentrations of reactants (methane and steam) and products (hydrogen, carbon monoxide, and carbon dioxide) were varied at atmospheric pressure, with the effects of temperature (525-700 °C) and residence time also being investigated. A power law rate model was developed using nonlinear regression to provide a predictive capability for the rate of methane conversion over this catalyst, to be used for reactor design and technoeconomic analysis of process designs. In order to provide some mechanistic insight, and to compare this catalyst to other non-promoted Ni/AlO catalysts reported in the literature, a reaction mechanism consisting of five elementary steps, using a Langmuir-Hinshelwood type approach, was also considered. These five steps included: (i) CH adsorption, (ii) HO adsorption, (iii) surface reaction of adsorbed CH and HO to form CO and H, (iv) CO desorption, and (v) H desorption. Nonlinear regression was then used to fit each of the rate laws to the experimental data. From these results, the model that assumed CH adsorption to be the rate determining step provided the best fit of the experimental data. This finding is consistent with literature studies on non-promoted Ni/AlO catalysts, in which methane adsorption has been proposed to be the rate determining step during catalytic methane steam reforming. Both the power rate laws and the rate law assuming CH adsorption to be the rate determining step can be used as predictive tools for determining methane conversion for a given set of process conditions. Additionally, a rate expression that assumed the rate was only a function of methane partial pressure was considered, namely, $$rate = k*P_{{CH_{4} }}$$ , where $$k = k_{0} *e^{{^{{ - {\text{Ea}}/{\text{RT}}}} }}$$ , with P in units of Torr. This first-order-methane rate expression fit the data well, yielding an apparent activation energy over this catalyst of E = 93 kJ/mol and the pre-exponential rate constant of k = 7.67 × 10 mol/(g-cat s Torr CH). [ABSTRACT FROM AUTHOR]

NiO(8 %)/Ni,H-ZSM-5 + AlO (1:1) catalysts differing in metal-support interactions, which influenced the metal-to-acid ratios, were examined. The interactions were changed by modifying the method of zeolite and aluminium hydroxide combining and the method of Ni incorporation. The catalysts were characterised by ICP, XRD, N sorption, SEM, TEM, NH-TPD, Py-IR, TPR, H chemisorption and XPS. The effect of metal-support interactions was determined during n-C conversion in a continuous system at H:CH = 7:1 Nm/m, 0.1 MPa and LHSV = 1 h. It was found that over the catalysts with weaker Ni-alumina interactions ( n/ n, 3.2 × 10 and 4.8 × 10), selectivity to isomerisation products was by 10-35 % higher, and selectivity to high boiling hydrocarbons by 10-30 % lower than over the catalysts with stronger Ni-support interactions ( n/ n, 1.2 × 10 and 1.8 × 10). [ABSTRACT FROM AUTHOR]

Hydrogen production from glycerol reforming in liquid (aqueous phase reforming, APR) and vapor (steam reforming SR) phase over alumina-supported nickel catalysts modified with Ce, Mg, Zr and La was studied. Characterization of catalysts by temperature programmed reduction and XPS analyses revealed important structural effects: (i) the intercalation of Mg between nickel and alumina that inhibited the alumina incorporation to nickel phases, (ii) the close contact between Ni and Zr phases and, (iii) the close surface interaction of La and Ce ions with NiO phases. The catalytic activity of the samples studied in this work clearly indicated the different catalyst functionalities necessary to carry out aqueous-phase and vapor-phase steam reforming of glycerol. For aqueous phase reforming of glycerol, the addition of Ce, La and Zr to Ni/Al2O3 improves the initial glycerol conversions obtained over the Ni/Al2O3 supported catalyst. It is suggested that the differences in catalytic activities are related with geometric effects caused by the decoration of Ni phases by Ce and La or by the close interaction between Ni and Zr. In spite that nickel catalysts showed high APR activities at initial times on stream, all samples showed, independently of support, important deactivation rates that deactivate the catalysts after few hours under operation. Catalysts characterization after APR showed the oxidation of the active metallic Ni during reaction as the main cause of the observed deactivation. In the case of the glycerol steam reforming in vapor phase, the use of Ce, La, Mg and Zr as promoters of Ni based catalysts increases the hydrogen selectivity. Differences in activity were explained in terms of enhancement in: surface nickel concentration (Mg), capacity to activate steam (Zr) and stability of nickel phases under reaction conditions (Ce and La). [ABSTRACT FROM AUTHOR]

In this article we describe our recent efforts in the area of palladium- and nickel-catalysed aromatic substitution reactions. Main focus is on low cost and low waste production methods. The use of aromatic carboxylic anhydrides in the Heck reaction leads to a waste-free protocol. In addition these reactions are easy to work up as no ligands or bases are used. For Heck reactions where substrates or products do not tolerate high temperatures we found that use of a bulky phosphoramidite ( 13b) as ligand for palladium leads to a very fast reaction at low temperatures. Recycle of palladium in ligand-free Heck and Suzuki reactions is easily accomplished by treating the palladium black that precipitates at the end of the reaction on a carrier material with a small excess of I2 prior to its re-use in the next run. Use of aryl chlorides in the palladium- and nickel-catalysed formation of biaryls can be accomplished by using the nickel-catalysed coupling with arylzinc chlorides. Better still, it was possible to make use of the arylgrignard and use a catalytic amount of ZnCl2. Whereas the strength of these aromatic substitution reactions lies in their broad tolerance of functional groups, one exception was the Sonogashira reaction on 3-bromoaniline. The problem was solved by making use of in situ catalytic protection of the NH2 group with benzaldehyde. [ABSTRACT FROM AUTHOR]