Impacts of alkali or alkaline earth metals addition on reaction intermediates formed in methanation of CO2 over cobalt catalysts

Additives affect the physiochemical properties of the catalyst as well as the evolution of the reaction intermediates produced during the reaction process such as the methanation of CO₂. In this study, Co/Al₂O₃ catalysts modified with Na, K, Mg or Ca were prepared and the reaction intermediates formed during CO₂ methanation were investigated. The results showed that Na, K or Mg species reacted with alumina, forming Al(OH)₃ or MgAl₂O₄ spinel structure, leading to the re-structure of the catalysts and a remarkable decrease of the specific surface area. The increased alkalinity of the catalyst did not promote the catalytic activity for methanation but promoted CO formation. The addition of Na or K enhanced the affinity of the catalyst to the reaction intermediates of HCOO* and CO₃²⁻, slowing down their further reduction to CH₄ and leading to the lower catalytic activity. The evolution of HCOO* and CO₃²⁻ species strongly correlated with the catalytic activity, while the direct correlation between the capability for the absorbance of CO₂* as well as the C–O functionality and the catalytic activity was not found. In addition, the addition of Na or K to Co/Al₂O₃ could also induce the formation of a significant amount of the coke species in the nanotube form.     

Methanation of CO2 over alumina supported nickel or cobalt catalysts: Effects of the coordination between metal and support on formation of the reaction intermediates

This study focused on the potential coordination between nickel or cobalt and alumina in Ni/Al₂O₃ and Co/Al₂O₃ catalysts and the impacts on their catalytic performances in methanation of CO₂. The results exhibited that Co/Al₂O₃ catalyst was far more active than Ni/Al₂O₃ catalyst, due to the varied reaction intermediates formed in methanation. The DRIFTS results of methanation of CO₂ exhibited that, over bare alumina, bicarbonate, formate and carbonate were the main intermediate species, which could be formed at even 80 °C. Over unsupported Ni catalyst, the formaldehyde species (H₂CO*) and CO* species were dominated. Over the Ni/Al₂O₃ catalyst, however, the reaction intermediates formed were determined by alumina and accumulated on surface of the catalysts. The coordination effects between nickel and alumina in Ni/Al₂O₃ were thus not remarkable in terms of enhancing catalytic activity when compared to that in Co/Al₂O₃ catalyst. Over unsupported Co catalyst and the bare alumina, the reaction intermediates formed were roughly similar. Nevertheless, the combination of Co and alumina in Co/Al₂O₃ catalyst could effectively facilitate the conversion of bicarbonate, formate and carbonate species. CO₂ could be activated over metallic cobalt sites, which could migrate and integrate with the hydroxyl group in alumina to form bicarbonate and further to formate and CO* species, and be further hydrogenated over cobalt sites to CH₄. Such a coordination between alumina and cobalt species promoted the catalytic performances.     

Impacts of metal loading in Ni/attapulgite on distribution of the alkalinity sites and reaction intermediates in CO2 methanation reaction

Both metal sites and alkaline sites are essential parameters for a catalyst used in methanation of CO₂. This study investigated the impacts of the relative abundance of metal sites and alkaline sites on the catalytic performances of nickel-based catalyst with attapulgite, a natural mineral, as the support. The results showed that the increase of nickel loading to attapulgite significantly decreased the abundance of alkaline sites, remarkably enhanced the catalytic activity, and suppressed the formation of CO. The in situ DRIFTS characterization of the CO₂ methanation indicated that the alkaline sites favored formation of the oxygen-containing reaction intermediates such as CO1, –OH, 1CO₂, formate, carbonate and bicarbonate species. In comparison, metallic nickel species promoted their further hydrogenation to form CH₄. Besides the absorption/activation of 1CO₂ was more preferable on surface of metallic nickel, but not on the alkaline sites. The availability of the alkaline sites was not as important as the metallic nickel species for preparation of an efficient catalyst for CO₂ methanation.     

Zr promotion effect in CO2 methanation over ceria supported nickel catalysts

Carbon dioxide methanation is an interesting way to reduce greenhouse effect gases emission and, simultaneously, provide a renewable energy source of methane. Ceria and 15 at.% Zr-doped ceria supported nickel catalysts were characterized by means of various techniques (BET, XRD, Raman, H₂-TPR, CO₂-TPD, O₂-TPO, OSC and H₂-chemisorption) and evaluated in carbon dioxide methanation. Zr incorporation into catalyst formulation reduced catalyst's basicity but favored its reducibility, nickel availability and oxygen storage capacity. These characteristics gave rise to an improved catalytic performance both in terms of activity and stability: temperature required to achieve 50% conversion was reduced in 20 °C and low temperature (250 °C) stability was improved in around 8%. Initial rates approach was employed to determine reaction rates and apparent activation energies for CO₂ methanation, which resulted in 113 and 121 kJ mol⁻¹for Ni/CeO₂ and Ni/Ce_0.85Zr_0.15O₂, respectively.     

Methanation of CO2 over Ni/Al2O3 modified with alkaline earth metals: Impacts of oxygen vacancies on catalytic activity

This study investigates the impacts of the alkaline earth metal (Mg, Ca, Sr, Ba) additives on properties and performances of nickel catalysts for CO₂ methanation. The results show that addition of Mg, Sr, and Ba creates more pores while Ca addition leads to merge of small pores. The alkalinity of the catalyst increases with the addition of Mg, Ca, Sr or Ba, however, it does not necessarily enhance the catalytic activity. The degree of reduction of nickel species is another important factor affecting catalyst activity. Mg or Ca addition promotes the reverse water gas shift reaction to form more CO but not the methanation. In converse, with the addition of Sr or Ba, the activities for methanation increased drastically, especially in the low temperature region. In situ Diffuse Reflection Infrared Fourier Transform Spectroscopy (DRIFTS) studies show that *OH, *CO₃, *CO₂, CH_x, HCOO*, *CO and H₂CO* species are main reaction intermediates. Mg or Ca promotes the carbonate formation. Sr or Ba promotes *CO and H₂CO* formation, which are the important reaction intermediates in the conversion of CO₂ to CH₄. In addition, the Electron Paramagnetic Resonance (EPR) characterization shows that the catalyst modified with Sr species generates the oxygen vacancies that prevent electrons from being paired, forming a Lewis basic position. The oxygen vacancies generated are crucial for enhancing the catalytic activities for methanation at the low reaction temperatures.     

Influence of the supports ZrO2 on selective methanation of CO over the nickel supported catalysts

It is attempted to optimize preparation of ZrO₂ as support of the nickel catalysts for selective methanation of CO in H₂-rich gas (CO-SMET). Therefore, the supports ZrO₂ were prepared at first by thermal decomposition method from zirconium oxynitrate and zirconium oxychloride at the calcination temperature of 400 °C and 800 °C, respectively. It is illustrated that the salt kind and calcination temperature affected phase state (tetragonal, monoclinic), crystallite size and specific surface area (SSA) of the supports. The difference in property of the supports influenced catalytic performance of the catalysts Ni/ZrO₂ for CO-SMET reaction. Especially, the chlorine ion residues in the support ZrO₂ prepared from zirconium oxychloride was beneficial for CO removal selectively. Furthermore, a precipitation method was adopted to prepare ZrO₂ for comparison with the thermal decomposition method with use of the zirconium oxychloride as starting material. It is found that the supports ZrO₂ prepared by the precipitation method induced a better dispersion of metallic Ni on its surface. The catalyst Ni/ZrO₂ with use of the support ZrO₂ prepared by the precipitation method and calcination at 400 °C exhibited a good performance at the reaction temperature of 220 °C in the 100 h durability test, where CO outlet concentration was kept below 10 ppm and the selectivity remained constant at 100%. Relation of Ni crystallite size and chlorine ion residues with the catalytic performance was discussed.     

Hydrogen production via the glycerol steam reforming reaction over nickel supported on alumina and lanthana-alumina catalysts

In the present work, a comparative study of Ni catalysts supported on commercially available alumina and lanthana-alumina carriers was undertaken for the glycerol steam reforming reaction (GSR). The supports and/or catalysts were characterized by PZC, BET, ICP, XRD, NH₃-TPD, CO₂-TPD, TPR and SEM. Carbon deposited on the catalytic surface was characterized by SEM, TPO and Raman. Concerning the Ni/LaAl sample it can be concluded that the presence of lanthana by: (a) facilitating the active species dispersion, (b) strengthening the interactions between nickel species and support, (c) increasing of the basic sites' population and redistributing the acid ones in terms of strength and density, provides a catalyst with improved performance for the GSR reaction, in terms of activity, H₂ production and long term stability. TPO and Raman indicate that the carbon on the Ni/LaAl catalyst was mostly amorphous and was deposited mainly on the support surface. For the Ni/Al catalyst, graphitic carbon was prevalent and likely covered its active sites.     

The influence of nickel content on the performance of hydrotalcite-derived catalysts in CO2 methanation reaction

A series of mixed oxides obtained by thermal decomposition of hydrotalcites containing different amounts of Ni and constant M^II+/M^III+ molar ratio were characterized by XRD, XANES, XES, H₂-TPR, CO₂-TPD, elemental analysis and low temperature nitrogen sorption technique. The results confirm the formation of periclase-like structured materials after thermal treatment, with nickel present as NiO in octahedral coordination environment. As proven by H₂-TPR with increasing Ni content the interaction between Ni and hydrotalcite matrix weakens, which has a positive influence on the catalytic performance. The catalysts containing different amounts of nickel (10.3, 16.2, 27.3, 36.8, 42.5 wt.%) showed at 300 °C a very good catalytic performance in carbon dioxide methanation, with CO₂ conversion of 36 (Ni10.3)–82% (Ni42.5) and CH₄ selectivity of 98–99%.     

Unveiling the promotion effect of Zr species on SBA-15 supported nickel catalysts for CO2 methanation

Introducing promoters on Ni-based catalysts for CO₂ methanation have been proved to be positive for enhancing their performance. And the correlation of the promotion mechanism and the reaction pathway is significant for designing efficient catalysts. In this contribution, series of Zr species promoted SBA-15 supported Ni catalysts were prepared by citric acid complexation method under a range of Zr/Ni atomic ratios from 0 to 2.5. In situ and ex situ characterizations were carried out. It was found that the addition of citric acid was conductive to improve CH₄ selectivity due to the higher concentrations of Ni⁰ confined in SBA-15, harvesting sufficient H atoms for CH₄ formation following formate pathway via a formyl intermediate. Furthermore, a coverage layer of Zr species was found on the support at Zr/Ni = 1.7, which interacted with the Ni particles, providing higher concentrations of medium basic sites for CO₂ activation. Accordingly, the optimum catalytic performance was obtained on ZrNi-1.7(CI), achieving CO₂ conversion as high as 78.1% and nearly 100% CH₄ selectivity at 400 °C, following the formate hydrogenation pathway. In addition, the ZrNi-1.7(CI) showed good stability owing to the confinement effect of SBA-15 and the Ni–Zr interaction, no carbon deposits were detected after 50 h test.     

Syngas production via the biogas dry reforming reaction over Ni supported on zirconia modified with CeO2 or La2O3 catalysts

The catalytic efficiency and bench scale time on steam stability of Ni dispersed on three commercially available catalytic supports (ZrO₂, La₂O₃–ZrO₂ and CeO₂–ZrO₂) has been studied for the dry reforming of methane (DRM) in the temperature range of 500–800 °C and a CH₄/CO₂ ratio equal to 1.5, simulating typical biogas quality. Ni supported on LaZr and CeZr carriers that obeyed enhanced basicity and oxygen ion lability values than Zr, exhibited superior catalytic efficiency and stability. A variety of techniques, namely N₂ physisorption-desorption (BET method), powder X-ray diffraction (XRD), hydrogen temperature programmed reduction (H₂-TPR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, potentiometric titration and inductively coupled plasma emission spectroscopy (ICP), were applied for the characterization of particles morphology, textural, structural and other physical properties of the materials, as well as the type of carbon deposited on the catalytic surface after exposure to DRM reaction conditions. Post-reaction analysis of the deposited carbon on the catalysts surfaces showed that the prominent trend of the carbon deposits on the Ni/Zr and Ni/LaZr samples was to have a filamentous tube like morphology (graphite-2H). In contrast, on the Ni/CeZr used catalyst, the formation of small amount of carbon tube-like architectures was detected. The enhanced basicity and Ni dispersion of the Ni/LaZr and Ni/CeZr samples as well as the high oxygen ion lability of the lattice oxygen in the latter, were considered to be the major factors involved in the superior efficiency and durability of these samples in comparison to Ni/Zr sample.     

Ni/Al2O3 catalysts for CO2 methanation: Effect of silica and nickel loading

Samples containing from 1 to 33 wt.% of NiO on silica and alumina doped with silica (1 and 20 wt.% silica in the support) have been prepared and characterized by BET, XRD, FT-IR, UV–vis–NIR, FE-SEM, EDXS, and TPR techniques. Catalysts have been pre-reduced in situ before catalytic experiments and data have been compared with Ni/Al₂O₃ reference sample. Characterization results showed that SiO₂ support has a low Ni dispersion ability mainly producing segregated NiO particles and a small amount of dispersed Ni²⁺ in exchange sites. Instead, for the Si-doped alumina a “surface spinel monolayer phase” is formed by increasing Ni loading and, only when the support surface is completely covered by this layer, NiO is formed. Moreover, H₂-TPR results indicated that NiO particles are more easily reduced compared to Ni species. Low loading Ni/SiO₂ catalysts show high selectivity and moderate activity for RWGS (reverse Water Gas Shift) reaction, likely mainly due to nickel species dispersed in silica exchange sites, as evidenced by visible spectroscopy. High loading Ni/SiO₂ catalysts show both methanation and RWGS but evident short-term deactivation for methanation, attributed to large, segregated Ni metal particles, covered by a carbon veil. Ni on alumina -rich carriers, where nickel disperses forming a surface spinel phase, show high activity and selectivity for methanation, and short-term catalyst stability as well. This activity is attributed to small nickel clusters or metal particles interacting with alumina, formed upon reaction. The addition of SiO₂ in Al₂O₃ support decreases the activity of Ni catalysts in CO₂ methanation, because it reduces the ability of the support to disperse nickel in form of the surface spinel phase, thus reducing the amount of Ni clusters in the reduced catalysts.     

Impact of Ce-Loading on Ni-catalyst supported over La2O3+ZrO2 in methane reforming with CO2

This paper investigated the effect of doping Ni supported catalysts with different ceria loading. The catalysts (5%Ni+x%Ce/La₂O₃+ZrO₂, where x = 0, 1, 2, 2.5, 3, 5) were synthesized via the wet impregnation technique and tested for methane reforming with carbon dioxide at atmospheric pressure, 700 °C and 42, 000 ml/g_cat.h gas hourly space velocity. The fresh catalysts were subjected to different characterization techniques such as X-ray diffraction, Surface area and pore analysis, H₂-temperature programmed reduction, CO₂-temperature programmed desorption and thermogravimetric analysis (TGA). A fine correlation between characterization results and catalytic activity is found. The results of the reactions indicated that 5%Ni/La₂O₃+ZrO₂ has the lowest conversion which increased with the percentage loading of CeO₂ up to 2.5 wt % and then began to decline. This suggests that 2.5 wt % loading is the optimum for CH₄ and CO₂ conversion. This particular catalyst composition has NiO species that could be reduced easily, as well as dense and wide distribution of all type of basic sites with respect to other catalyst system. The used catalysts were again subjected to TGA and RAMAN analysis where the least carbon deposition and the least deactivation factor was observed for 5%Ni+5%Ce/La₂O₃+ZrO₂ catalysts.     

Catalytic gasification of food waste in supercritical water over La promoted Ni/Al2O3 catalysts for enhancing H2 production

Ni/Al₂O₃ catalyst is the one of promising catalysts for enhancing H₂ production from supercritical water gasification (SCWG) of biomass. However, due to carbon deposition, the deactivation of Ni/Al₂O₃ catalyst is still a serious issue. In this work, the effects of lanthanum (La) as promoter on the properties and catalytic performance of Ni/Al₂O₃ in SCWG of food waste were investigated. La promoted Ni/Al₂O₃ catalysts with different La loading content (3–15 wt%) were prepared via impregnation method. The catalysts were characterized using XRD, SEM, BET techniques. The SCWG experiments were carried out in a Hastelloy batch reactor in the operating temperature range of 420–480 °C, and evaluated based on H₂ production. The stability of the catalysts was assessed by the amount of carbon deposition on catalyst surface and their catalytic activity after reuse cycles. The results showed that 9 wt% La promoter is the optimal loading as Ni/9La–Al₂O₃ catalyst performed best performance with the highest H₂ yield of 8.03 mol/kg, and H₂ mole fraction of 42.46% at 480 °C. La promoted Ni/Al₂O₃ catalysts have better anti-carbon deposition properties than bare Ni/Al₂O₃ catalyst, resulting in better gasification efficiency after reuse cycles. Ni/9La–Al₂O₃ catalyst showed high catalytic activity in SCWG of food waste and had good stability as it was still active for enhancing H₂ production when used in SCWG for the third time, which indicated that La promoted Ni/Al₂O₃ catalysts are potential additive to improve the SCWG of food waste.     

Effect of the Rare Earth Metals (Tb,Nd, Dy) addition for the modification of nickel catalysts supported on alumina in CO2 Methanation

In the current research, a group of rare-earth metals functionalized mesoporous Ni-M/Al₂O₃ (M = Tb, Dy, Nd) composite oxides were prepared by the one-pot sonochemical pathway and applied in the CO₂ methanation procedure. Promoters can partially influence the textural and catalytic characteristics of Ni–Al₂O₃ catalysts. Physicochemical characteristics of the as-fabricated catalysts were identified utilizing X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Energy-dispersive X-ray spectroscopy (EDS), Temperature Programmed Reduction (H₂-TPR), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) analyses. Among the specimens, the catalyst modified by Terbium (Tb) manifested better catalytic performance and CH₄ selectivity, particularly at low temperatures (350–400 °C). The influence of reaction temperature (200–500 °C) was scrutinized below space velocity (GHSV) of 25,000 ml/g_cath, atmospheric pressure, and stoichiometric ratio of CO₂ to H₂ (1: 4). The impact of the desired content of nickel and terbium was examined. The 25Ni–5Tb–Al₂O₃ operates the best function for CO₂ methanation, which can attain the highest CO₂ conversion of 66.93% at 400 °C at atmospheric pressure. The superior catalytic performance of 25Ni–5Tb–Al₂O₃ could be assigned to the appropriate fabrication method and the promotion effect of Terbium. The synthesis effect could be assigned to its large surface area, obtaining by the hot spot mechanism. The addition of Terbium promotes the Ni distribution on the supports as well as accelerates the positive reaction due to the oxygen vacancies of Terbium. Besides, these outcomes could be defined with the maximum distribution of active nickel sites on the catalyst and improvement in the catalyst reduction ability at low temperatures.     

Insight into the role of Fe on catalytic performance over the hydrotalcite-derived Ni-based catalysts for CO2 methanation reaction

A series of Fe modified hydrotalcite-derived Ni-based catalysts (Ni₃Fe_x-calc) were synthesized to evaluate the effect of Fe on CO₂ methanation performance over Ni₃-calc catalyst. The results showed that Ni₃–Fe_0.5-calc had superior catalytic activity with 78% CO₂ conversion rate at 200 °C. The addition of moderate amount of Fe can effectively improve the reducibility, enrich the medium basic sites of Ni₃-calc catalyst, and further facilitate the adsorption and activation of CO₂. This resulted in the outstanding low-temperature CO₂ methanation activity, as well as the enhanced resistance of carbon deposition. In-situ DRIFTS results indicated that the CO₂ methanation reaction mechanism involved a progressive hydrogenation of carbonate and formate species to methane route. The formate species was the main intermediates during CO₂ methanation. The introduction of Fe could significantly accelerate the hydrogenation rate of carbonates and formate species.     

Modification of silica supported nickel catalysts with lanthanum for stability improvement in methane reforming with CO2

Dry reforming of methane (DRM) with excessive methane composition at CH₄/CO₂ = 1.2:1 was studied over lanthanum modified silica supported nickel catalysts (Ni-xLa-SiO₂, x: 1, 2, 4, and 6% in the target weight percent of La). The catalysts were prepared by ammonia evaporation method. Nickel phyllosilicate and La₂O₃ were the main phases in calcined catalysts. The modification of La enhanced the formation of 1:1 and Tran-2:1 nickel-phyllosilicate. There existed an optimum content of La loading at 1.50 wt% in Ni–2La–SiO₂ which resulted in its highest reduction degree (95.3%). The catalysts with appropriate amounts of La exhibited higher amount of CO₂ adsorption and created more medium and strong base centers. The sufficient number of exposed metallic nickel sites to catalyze the reforming reaction, as well as enough medium and strong basic sites in Ni–La–SiO₂ interface to accomplish the carbon removal were two important factors to attenuate catalyst deactivation. The catalyst stability evaluated at 750 °C for 10 h followed the order: Ni–2La–SiO₂ > Ni–4La–SiO₂ > Ni–1La–SiO₂ ≈ Ni–6La–SiO₂ > Ni–SiO₂. Ni–2La–SiO₂ catalyst possessed the lowest deactivation behavior, whose CH₄ conversion dropped from 60.2 to 55.9% after 30 h operation at 750 °C, indicating its high resistance against carbon deposition and sintering.     

Combined steam and CO2 reforming of methane over one-pot prepared Ni/La-Si catalysts

The highly dispersed mNi/xLa−Si catalysts with varied weight percentages of Ni and La were synthesized via one-pot sol-gel process and subsequently applied to combined carbon dioxide and steam reforming of methane (CSDRM) for syngas production. The addition of La improved the catalytic activity and stability as well as the coke resistance of the mNi/xLa−Si catalysts. The effects of preparation routes, Ni contents and CO₂/steam (C/S) ratios on the performances of the Ni/LaSi catalysts were studied in detail for the CSDRM. The 17.5Ni/3.0LaSi catalyst synthesized with the assistance of poly (ethylene glycol) and ethylene glycol exhibited the most excellent catalytic activity, stability and coke resistance. In addition, the H₂/CO ratios in the product gas could be tuned by changing the C/S ratios in the feed. When the C/S ratio was 0.5, the H₂/CO ratio of about 2 was achieved for the 17.5Ni/3.0LaSi catalyst.     

Steam reforming of acetic acid over NiKOH/Al2O3 catalyst with low nickel loading: The remarkable promotional effects of KOH on activity

In this paper, the effects of strong base (KOH) addition on the catalytic performances of Ni/Al₂O₃ catalysts in acetic acid steam reforming for hydrogen generation was investigated. The addition of KOH drastically changed the physiochemical property and catalytic performances of the nickel–based catalysts. KOH reacted with γ–Al₂O₃ during calcination, forming ɑ–Al₂O₃ with Al(OH)₃ as a reaction intermediate, which led to reconstruction of the porous structure, merge of small pores, decreased specific area and sintering of nickel. Most importantly, the catalytic activity of nickel–based catalysts were significantly enhanced by the addition KOH, especially the ones with low nickel loading. There are almost no active of 1 wt% Ni/Al₂O₃ catalyst for steam reforming of acetic acid, while, with adding 5 wt % KOH, activity of the catalyst matched that of 20 wt% Ni/Al₂O₃. In–situ DRIFTS study showed the involvement of the reactive intermediates including CH₃, CH₂, CO, COO, COC, CC and absorbed CO₂ in acetic acid steam reforming. The Ni/Al₂O₃ catalyst with low nickel loading had insufficient metallic nickel to gasify these reactive intermediates. The presence KOH effectively aided gasification of the reactive intermediates, and thus significantly promoted the catalytic activity. In addition, the KOH with varied loading significantly affect formation of catalytic coke and polymeric coke formed during the reforming reaction.     

CO2 methanation over nanocrystalline Ni catalysts supported on mechanochemically synthesized Cr2O3-M (M=Fe,Co, La,and Mn) carriers

In the present study, a series of Cr₂O₃ powders modified by different promoters such as Fe, Co, La, and Mn were synthesized using a facile and solvent-free mechanochemical method and the prepared powders were used as a catalyst carrier for the preparation of 20 wt%Ni catalysts in CO₂ methanation. The results indicated that among all catalysts, the nickel catalyst supported on the Mn-promoted Cr₂O₃ exhibited the best catalytic performance. The results showed that there was an optimum for the Mn content and the increment in Mn content up to 15 wt% improved the catalytic performance due to its positive influence on increasing nickel dispersion and catalyst reducibility. The 20 wt%Ni/15 wt%Mn–Cr₂O₃ catalyst possessed a CO₂ conversion of 72.12% and CH₄ selectivity of 100% at 350 °C (H₂/CO₂ = 3 M ratio, GHSV = 18,000 ml/g_cat.h) with high stability during 12 h on stream. The obtained results showed that the increment in H₂/CO₂ molar, and the decrement in GHSV value and calcination temperature improved the catalytic performance.     

Hydrogen production from glycerol steam reforming over nickel catalysts supported on alumina and niobia: Deactivation process,effect of reaction conditions and kinetic modeling

Ni catalysts were prepared by wet impregnation of three different supports: alumina, niobia and 10 wt.% niobia/alumina, prepared by (co)precipitation. The catalysts were evaluated on steam reforming of glycerol at 500 °C, for 30 h. The catalyst supported on Nb₂O₅/Al₂O₃ presented the best performance, with higher conversion into gas (80%) during all reaction time and hydrogen yield of 50%. Alumina supported catalyst showed higher deactivation and lower hydrogen yield. All catalysts showed coke formation, but it was formed in larger amount on the catalysts supported on single oxides. A depth study was conducted to evaluate the effect of reaction variables as space velocity, glycerol concentration in feed and temperature on the catalytic performance of the Nb₂O₅/Al₂O₃ catalyst. Kinetic study was also performed for this catalyst using two different approaches, obtaining glycerol and steam orders, as well as the apparent activation energy.