Alumina-supported Ni Catalysts Research Articles

Hydroconversion of lignin-derived platform compound guaiacol to fuel additives and value-added chemicals over alumina-supported Ni catalysts

Hydroconversion of guaiacol (GUA) over γ-Al2O3 and phosphatized-γ-Al2O3 (γ-Al2O3(P)) supported Ni catalysts was initiated by Lewis-sites and active Ni sites. Conversion proceeded via transmethylation and hydrodemethylation/hydrodemethoxylation as major and minor pathways, respectively, resulting in mainly catechol and methylcatechols, and via series of consecutive hydrodehydroxylation (HDHY) and ring hydrogenation (HYD) reactions leading to partially and fully deoxygenated, saturated, and unsaturated products. High Ni-loading and high H2 pressure promoted the formation of cyclohexane and methyl-substituted cyclohexanes; however, above 300 °C the hydrogenation–dehydrogenation equilibrium favored the formation of benzene and methyl-substituted benzenes. Ni/γ-Al2O3(P) showed suppressed HYD/HDHY activity resulting in pronounced formation of catechol and/or phenol and their methyl-substituted derivatives. Surface phenolate species were substantiated as surface intermediates of hydrodeoxygenation. Phosphatizing reduced the concentration of both basic OH and Lewis acid (Al+) – Lewis base (O–) pair surface sites of the γ-Al2O3 support and, thereby, suppressed phenolate formation and hydrodeoxgenation.

External [1 1 1] facets on nanorod gamma alumina boosts catalytic reductive amination of carbonyl compound to primary amine

Hydrogen spillover had played a significant role in catalytic processes involving reducible oxide supported metal catalyst and hydrogen molecule. Herein, crystal plane regulative hydrogen spillover strategy for the effective reductive amination on Ni/Al2O3 was developed. A rod-like alumina supported Ni catalyst with primarily external (111) facets was prepared. In the presence of NH3 and H2, Ni/Al2O3 (111) exhibited a turnover number of 30.4 h−1, which was 136-fold higher than that of Ni/Al2O3 (110) in the reductive amination of furfural to furfuryl amine. For the Ni/Al2O3 (111) catalyst, Al2O3 (111) facets exhibited strong Lewis acidity, resulting in an enhanced H affinity of Al2O3 (111) and a positively charged of Ni through electronic interaction. It was revealed that strong H affinity of Al2O3 (111) and positively charged Ni sites significantly promoted hydrogen migration from Ni surface to Al2O3 (111) facets, which effectively prevented the Ni sites from hydrogen poisoning and enhanced the adsorption and activation of NH3 and intermediates for reductive amination. Consequently, the activation energy of Schiff base reductive ammonolysis was obviously reduced, resulting in high inherent activity for furfural reductive amination to furfuryl amine. This work developed a new strategy for high efficiency reductive amination catalyst in terms of hydrogen spillover effect.

The rate determining steps and rate equation for the oxidative dry reforming of methane over supported Ni catalyst

Dry reforming of methane (DRM) and its modification with O2 co-feed, the ODRM reaction, have been gaining importance. However, a general rate equation applicable for the ODRM reaction with varying O2 co-feed has not been reported. This general rate equation should be applicable for the DRM and ODRM reactions depending on the amount of O2 co-feed. Microkinetic models simulate catalytic reactions without making any a priori assumptions for the RDS and are helpful in developing rate equations. Unfortunately, microkinetic modelling for ODRM over supported monometallic Ni has not been carried out. Here, we perform microkinetic modelling using an existing reforming reaction mechanism for ODRM over an alumina-supported Ni catalyst. Validation is achieved by comparing experimental and microkinetic outlet flow rates at different feed rates of O2 and applying R2 analysis and F-tests. Once the model is validated, we identify the RDS through a hierarchical strategy using microkinetic results and sensitivity analysis for varying amounts of O2 co-feed. The results reveal that CH4 activation is the RDS. CH4 activation can occur through direct dehydrogenation on an empty site or oxidative dehydrogenation aided by adsorbed O, depending on the amount of O2 co-feed. Once the RDSs are identified, we derive a general rate equation that effectively simulates the DRM reaction with different amounts of O2 co-feed. We further examine the effect of the amounts of O2 co-feed and ascertain the presence of maximum hydrogen production for certain amounts of O2 co-feed.

Fe-Promoted Alumina-Supported Ni Catalyst Stabilized by Zirconia for Methane Dry Reforming

The dry reforming of methane is a highly popular procedure since it can transform two of the most abundant greenhouse gases, methane and carbon dioxide, into useful syngases that can be further processed into valuable chemicals. To successfully achieve this conversion for the effective production of syngas, an optimal catalyst with advantageous physicochemical features must be developed. In this study, a variety of Ni-based catalysts supported by zirconia alumina (5Ni-10Zr + Al) were prepared by using the impregnation approach. Different loadings of Fe promoter were used, and the performances of the resulting catalysts in terms of activity and stability were investigated. The catalyst used in this study had an active metal component made of 5% Ni and x% Fe supported on 10ZrO2 + Al2O3, where x = (1, 2, 3, and 4). The physicochemical characteristics of both freshly calcined and used catalysts were studied using a range of characterization techniques, such as: N2 adsorption–desorption isotherms, XRD, H2-TPR, Raman spectroscopy, TGA, and TEM. An investigation of the effects of the Fe promoter on the catalytic activity of the catalyst (5Ni + xFe-10Zr + Al) was conducted. Amongst the studied catalysts, the 5Ni + 3Fe-10Zr + Al catalyst showed the best catalytic activity with CH4 and CO2 conversions of 87% and 90%, respectively, and had an H2/CO ratio of 0.98.

Preparation of an Anodic Alumina-Supported Ni Catalyst and Development of a Catalytic Plate Reformer for the Steam Reforming of Methane

A plate-type Al/Fe–Cr alloy/Al-clad substrate was used to prepare a sandwich-structured plate-type anodic alumina catalyst by anodization, post-modification treatment, and metal loading. The as-prepared plate-type catalyst was utilized in the design of a catalytic plate reactor for a methane steam reforming reaction, and a 3D model was developed to simulate the performance of tube-type and box-type reformers. The experimental results of the preparation of the clad materials showed that the hydrothermal treatment and subsequent high-temperature calcination transformed the amorphous skeletal alumina in the conventional anodic alumina layer into γ-alumina, and significantly increased its specific surface area. Simulation results showed that the temperature difference between the channel wall and the center of the gas phase of the thin-walled catalyst was only 30% of that of the particulate catalyst, indicating the potential advantages of the catalytic plate reactor in terms of heat transfer and energy saving. When the length-to-diameter ratio (or length-to-width ratio) of the reaction channel is small and the channel height is large, insufficient transverse mass transfer and backmixing are two major factors affecting reformer performance. For the tube-type channels, a length-to-diameter ratio of 10~35, and a diameter of 5~20 represent favorable choices. In contrast, for the box-type channel, the length-to-width ratio and the height should be set to 2~4 and 2~5 mm, respectively. Additionally, for box-type channels, the number of gas inlet ports has a significant effect on the reformer performance, and the distribution state provided by two inlet ports is close to the ideal distribution state.

Understanding the different deoxygenation reaction pathways of lauric acid over alumina-supported Ni and Co catalysts

Ni/Al2O3 and Co/Al2O3 perform differently in the conversion of aliphatic acids as evidenced by the preferred reaction pathways for both catalysts.

Structural Characterization of Nickel-Doped Aluminum Oxide Cations by Cryogenic Ion Trap Vibrational Spectroscopy.

Isolated nickel-doped aluminum oxide cations (NiOm)(Al2O3)n(AlO)+ with m = 1-2 and n = 1-3 are investigated by infrared photodissociation (IRPD) spectroscopy in combination with density functional theory and the single-component artificial force-induced reaction method. IRPD spectra of the corresponding He-tagged cations are reported in the 400-1200 cm-1 spectral range and assigned based on a comparison to calculated harmonic IR spectra of low-energy isomers. Simulated spectra of the lowest energy structures generally match the experimental spectra, but multiple isomers may contribute to the spectra of the m = 2 series. The identified structures of the oxides (m = 1) correspond to inserting a Ni-O moiety into an Al-O bond of the corresponding (Al2O3)1-3(AlO)+ cluster, yielding either a doubly or triply coordinated Ni2+ center. The m = 2 clusters prefer similar structures in which the additional O atom either is incorporated into a peroxide unit, leaving the oxidation state of the Ni2+ atom unchanged, or forms a biradical comprising a terminal oxygen radical anion Al-O•- and a Ni3+ species. These clusters represent model systems for under-coordinated Ni sites in alumina-supported Ni catalysts and should prove helpful in disentangling the mechanism of selective oxidative dehydrogenation of alkanes by Ni-doped catalysts.

The Characterisation of Hydrogen on Nickel and Cobalt Catalysts

We have investigated a series of supported and unsupported nickel and cobalt catalysts, principally using neutron vibrational spectroscopy (inelastic neutron scattering, INS). For an alumina supported Ni catalyst we are able to detect hydrogen on the metal for the first time, all previous work has used Raney Ni. For an unsupported Ni foam catalyst, which has similar behaviour to Raney Ni but with a much lower density, the spectra show that there are approximately equal numbers of (100) and (111) sites, in contrast to Raney Ni that shows largely (111) sites. The observation of hydrogen on cobalt catalysts proved to be extremely challenging. In order to generate a cobalt metal surface, reduction in hydrogen at 250–300 °C is required. Lower temperatures result in a largely hydroxylated surface. The spectra show that on Raney Co (and probably also on a Co foam catalyst), hydrogen occupies a threefold hollow site, similar to that found on Co(10bar{1}0). The reduced surface is highly reactive: transfers between cells in a high quality glovebox were sufficient to re-hydroxylate the surface.

Rational design of nickel-based catalyst coupling with combined methane reforming to steadily produce syngas

Inhibiting the aggregation of Ni particles and coke deposition on supported nickel catalysts has always been an enormous challenge in methane reforming to syngas. To address the problem, in this study, a Ce-Al-O supported Ni mesoporous catalyst (Ni/Ce-Al-O-A) was designed and synthesized by using evaporation-induced self-assembly (EISA) method and citric acid auto-reduction (AR) method, respectively. The prepared Ni/Ce-Al-O-A catalyst, without further reduction, was used for combined methane dry reforming comprising CO2 dry reforming of methane (DRM) and methane partial oxidation (MPO) to effectively produce syngas. Employing citric acid auto-reduction method for catalyst preparation directly led to the formation of metallic Ni by calcining the precursor of Ni/Ce-Al-O-A in argon atmosphere, with high dispersion and small particle size (at around 4.5 nm) of metallic Ni being obtained. The Ni/Ce-Al-O-A catalyst presented high catalytic activity, better than those of reference catalyst prepared by general impregnation method and the commercial alumina supported Ni catalyst synthesized by citric acid auto-reduction method. In a 250 h lifetime test, the Ni/Ce-Al-O-A catalyst exhibited an extremely catalytic stability and anti-coking ability, and no deactivation was observed. The excellent catalytic activity of Ni/Ce-Al-O-A catalyst was mainly attributed to the Ce-incorporated Ce-Al-O that facilitated the adsorption and activation of CO2 as well as the combined methane reforming (DRM-MPO) in which the existing oxygen could effectively inhibit the coke formation.

Hydrogen and/or syngas production by combined steam and dry reforming of methane on nickel catalysts

Two alumina supported Ni catalysts with pore sizes of 5.4 nm and 9 nm were synthetized, characterized and tested in the Combined Steam and Dry Reforming of Methane (CSDRM) for the production of hydrogen rich gases or syngas. The reaction mixture was designed to simulate the composition of real clean biogas, the addition of water being made in order to have molar ratios of H2O:CO2 corresponding to 2.5:1, 7.5:1 and 12.5:1. Structural and functional characterization of catalysts revealed that Ni/Al2O3 with larger pore size shows better characteristics: higher surface area, lower Ni crystallite sizes, higher proportion of stronger catalytic sites for hydrogen adsorption, and higher capacity to adsorb CO2. At all studied temperatures, for a CH4:CO2:H2O molar ratio of 1:0.48:1.2, a (H2+CO) mixture with H2:CO ratio around 2.5 is obtained. For the production of hydrogen rich gases, the optimum conditions are: CH4:CO2:H2O = 1:0.48:6.1 and 600 °C. No catalyst deactivation was observed after 24 h time on stream for both studied catalysts, and no carbon deposition was revealed on the used catalysts surface regardless the reaction conditions.

A comparative study of catalytic behaviors of Mn, Fe, Co, Ni, Cu and Zn–Based catalysts in steam reforming of methanol, acetic acid and acetone

This study investigated the distinct catalytic behaviors of mono Mn, Fe, Co, Ni, Cu and Zn catalysts in the reforming of the small organics including methanol, acetic acid and acetone. The results showed that Mn, Fe or Zn-based catalysts showed almost no activity for steam reforming of either methanol, acetic acid or acetone, due to their low capacity to break the chemical bonds of the organics or to activate steam. Co and Cu-based catalysts were generally active for steam reforming of methanol. Nevertheless, Co-based catalysts promoted methanol decomposition to form a substantial amount of CO. Alumina as a support remarkably influenced catalytic stability of the catalyst. The unsupported Cu catalyst showed a much lower stability than Cu/Al2O3. Nevertheless, the unsupported Ni was more stable than Ni/Al2O3 catalyst, due to its high resistivity towards coking. The unsupported Co, however, was prone to coking. The C/H ratios in the coke formed over the unsupported and alumina-supported Ni or Co catalysts were distinct, indicating the involvement of alumina in the coking process. In addition, Ni and Co catalysts behaved differently. Ni/Al2O3 showed a superior stability than Co/Al2O3 in steam reforming of acetone. The coke formed on Ni/Al2O3 was more aromatic than that over Co/Al2O3 catalysts while morphologies of coke (nanotubes over Ni/Al2O3 versus fibrous coke over Co/Al2O3) were also different.

Steam reforming of acetic acid for hydrogen production over attapulgite and alumina supported Ni catalysts: Impacts of properties of supports on catalytic behaviors

In this study, the potential of attapulgite (ATTP) as the support of nickel catalysts for steam reforming of acetic acid to produce hydrogen were evaluated. Ni/Al2O3 was prepared and evaluated for comparison. The results showed that ATTP had a much lower specific surface area and a lower thermal stability than alumina. Nevertheless, the interaction between nickel and ATTP was much weaker than that of nickel with alumina. As a result, the Ni/ATTP catalyst had superior activity than the Ni/Al2O3 catalyst, especially at low nickel loading. Ni/Al2O3 was more stable than Ni/ATTP. The fibrous coke, which was probably catalytic coke, formed over Ni/Al2O3 did not cause the rapid deactivation of the catalyst, while the amorphous coke formed over Ni/ATTP catalyst, which was probably the polymeric coke, rapidly deactivated the catalyst. The coke species contained COOH, CO, aliphatic structure and aromatic ring structures. In addition, the effects of these two carriers on the steam reforming mechanism were investigated by the in-situ DRIFTS.

Effect of impregnation sequence of Mg on performance of mesoporous alumina supported Ni catalyst in dry reforming of methane

In this study, effect of Mg impregnation sequence on the activity of the mesoporous alumina supported Ni catalysts was investigated in dry reforming of methane. Characterization and activity test results showed that Mg incorporation sequence significantly influenced the physicochemical properties and the activity of the catalyst as well as coke deposition during reforming reaction. The synthesized catalysts were characterized by x-ray diffraction, N2 adsorption, temperature programmed reduction, scanning electron microscopy, CO2-temperature programmed desorption, inductively coupled plasma optical emission spectrometry, x-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy (FTIR) and pyridine adsorbed diffuse reflectance FTIR spectroscopy techniques. Mg incorporation altered the reduction profile of the monometallic catalyst and increased the reduction temperature of the nickel particles. XRD diffraction peaks corresponding to γ-A2O3 and α-Al2O3, as well as nickel-magnesium spinels and metallic Ni were observed depending on Mg incorporation sequence. The monometallic Ni catalyst showed higher activity than the bimetallic NiMg catalysts. However, coke formation was significantly influenced as a result of synthesis route. Total organic carbon, thermogravimetric analysis and SEM images exhibited that the highest coke formation was obtained over the catalyst which was prepared by sequential impregnation of Mg and then Ni. Almost no coke formation was observed on the spent catalyst, which was synthesized by simultaneously impregnation of Mg and Ni, due to the high interaction between Ni and Mg with the formation of a NiOMgO solid solution during the high calcination temperature.

CO and CO2 methanation over Ni catalysts supported on alumina with different crystalline phases

The effect of alumina crystalline phases on CO and CO2 methanation was investigated using alumina-supported Ni catalysts. Various crystalline phases, such as α-Al2O3, θ-Al2O3, δ-Al2O3, η-Al2O3, γ-Al2O3, and κ-Al2O3, were utilized to prepare alumina-supported Ni catalysts via wet impregnation. N2 physisorption, H2 chemisorption, temperature-programmed reduction with H2, CO2 chemisorption, temperature-programmed desorption of CO2, and X-ray diffraction were employed to characterize the catalysts. The Ni/θ-Al2O3 catalyst showed the highest activity during both CO and CO2 methanation at low temperatures. CO methanation catalytic activity appeared to be related to the number of Ni surface-active sites, as determined by H2-chemisorption. During CO2 methanation, Ni dispersion and the CO2 adsorption site were found to influence catalytic activity. Selective CO methanation in the presence of excess CO2 was performed over Ni/γ-Al2O3 and Ni/δ-Al2O3; these substrates proved more active for CO methanation than for CO2 methanation.

Mo-promoted Ni/Al2O3 catalyst for dry reforming of methane

Mo-promoted alumina supported Ni catalysts were prepared through a conventional impregnation method and tested in dry reforming of methane (DRM) at temperatures from 550 to 850 °C. The catalysts were characterized by means of H2-temperature programmed reduction (H2-TPR), CO2-temperature programmed desorption (CO2-TPD), X-ray diffraction (XRD), N2 physisorption and Raman spectroscopy. Mo-promotion caused a reduction in the DRM catalytic activity. The weaker interaction between NiO species and the alumina support, the formation of a MoNi4 phase, and the lower basicity of this Ni-Mo/Al2O3 catalyst were identified as the main causes for its lower activity. However, pre-reducing the Ni-Mo/Al2O3 catalyst at temperatures lower than 700 °C, instead of 900 °C, resulted in a considerable increase of its catalytic activity. This was mainly due to the formation of a separate Ni0 phase that did not interact with Mo and to an increase in medium strength basicity.

A comparative study of alumina-supported Ni catalysts prepared by photodeposition and impregnation methods on the catalytic ozonation of 2,4-dichlorophenoxyacetic acid

The heterogeneous catalytic ozonation on unsupported and supported oxides has been successfully tested for the removal of several refractory compounds in aqueous solution. In this work, alumina-supported nickel catalysts prepared by photodeposition and impregnation methods were compared in the catalytic ozonation of 2,4-dichlorophenoxyacetic acid (2,4-D). The catalysts were characterized by high-resolution electron microscopy and X-ray photoelectron spectroscopy. The photochemical decomposition of Ni acetylacetonate to produce Ni(OH)2, NiO, and traces of Ni° deposited on alumina was achieved in the presence of benzophenone as a sensitizer. A similar surface composition was found with the impregnated catalyst after its reduction with hydrogen at 500 °C and exposed to ambient air. Results indicated a higher initial activity and maleic acid (byproduct) concentration with the photodeposited catalyst (1 wt% Ni) compared to the impregnated catalyst (3 wt% Ni). These findings suggest the use of the photodeposition method as a simple and reliable procedure for the preparation of supported metal oxide/metal catalysts under mild operating conditions.

Samarium Promoted Ni/Al2O3 Catalysts for Syngas Production from Glycerol Pyrolysis

The current paper reports on the kinetics of glycerol reforming over the alumina-supported Ni catalyst that was promoted with rare earth elements. The catalysts were synthesized via wet impregnation method with formulations of 3 wt% Sm-20 wt% Ni/77 wt% Al2O3. The characterizations of all the as-synthesized catalysts were carried out, viz. BET specific surface area measurements, thermogravimetri analysis for temperature-programmed calcination studies, FESEM for surface imaging, XRD to obtain diffraction patterns, XRF for elemental analysis, etc.. Reaction studies were performed in a stainless steel fixed bed reactor with reaction temperatures set at 973, 1023 and 1073 K employing weight hourly space velocity (WHSV) of 4.5×104 mL g-1 h-1. Agilent GC with TCD capillary column was used to analyze gas compositions. Results gathered showed that the BET specific surface area was 2.09 m2.g-1 for the unpromoted Ni catalyst while for the promoted catalysts, was 2.68 m2.g-1. Significantly, the BET results were supported by the FESEM images which showed promoted catalysts exhibit smaller particle size compared to the unpromoted catalyst. It can be deduced that the promoter can increase metal dispersion on alumina support, hence decreasing the size of particles. The TGA analysis consistently showed four peaks which represent water removal at temperature 373-463 K, followed by decomposition of nickel nitrate to produce nickel oxide. From reaction results for Sm promotion showed glycerol conversion, XG of 27% which was 7% higher than unpromoted catalyst. The syngas productions were produced from glycerol decomposition and created H2:CO product ratio which always lower than 2.0. The H2:CO product ratio of 3 wt% Sm promoted Ni/Al2O3 catalyst was 1.70 at reaction temperature of 973 K and glycerol partial pressure of 18 kPa and suitable enough for Fischer-Tropsch synthesis.

Hydrogen Production by Methane Dry Reforming on Supported Nickel Catalysts – Enhanced Stability of the Reforming Process

Dry reforming reaction of CH4 by CO2 was carried out over alumina-supported Ni catalysts. Main products were H2 and CO with small amount of H2O by-production because of reverse water gas shift reaction. The activity was gradually decreased with time on stream by carbon deposition. The addition of Ce component was investigated to improve the catalyst stability. The Ce addition brought decrease of carbon deposition during the reaction. The role of Ce has been considered that an inactive coke formation is significantly suppressed.

Mechanistic study of the effect of chlorine on selective CO methanation over Ni alumina-based catalysts

The effect of residual chlorine of alumina-supported Ni catalysts on the selective CO methanation reaction was investigated. By chloride addition to the catalyst, CO2 methanation and the reverse water gas-shift reaction were significantly suppressed in the course of the reaction. FTIR measurements for CO2 adsorption on a series of modified catalysts with various chlorine-containing additives revealed that chlorine suppressed the dissociation of CO2 on the catalyst surface, which led to the formation of adsorbed CO species. The FTIR results combined with TPD measurements for CO2 desorption indicates that chlorine adsorbed on Ni metal diminished the formation of carboxylate species on the same surface under flowing CO2 conditions. Through the present study, the controlling factor for the selective methanation of CO by chlorine was clarified in high CO2 concentration-containing hydrogen rich gas.

Production of CO-rich hydrogen gas from glycerol dry reforming over La-promoted Ni/Al2O3 catalyst

Dry reforming of glycerol has been carried out over alumina-supported Ni catalyst promoted with lanthanum. The catalysts were characterized using EDX, liquid N2 adsorption, XRD technique as well as temperature-programmed reduction. Significantly, catalytic glycerol dry reforming under atmospheric pressure and at reaction temperature of 1023 K employing 3 wt%La–Ni/Al2O3 catalyst yielded H2, CO and CH4 as main gaseous products with H2:CO < 2.0. Post-reaction, XRD analysis of used catalysts showed carbon deposition during glycerol dry reforming. Consequently, BET surface area measurement for used catalysts yielded 10–21% area reduction. Temperature-programmed gasification studies with O2 as a gasification agent has revealed that La promotion managed to reduce carbon laydown (up to 20% improvement). In comparison, the unpromoted Ni/Al2O3 catalyst exhibited the highest carbon deposition (circa 33.0 wt%).