Combustion synthesis of copper ceria solid solution for CO2 conversion to CO via reverse water gas shift reaction

The reverse water–gas shift chemical (RWGS) reaction is a promising technique of converting CO₂ to CO at low operating temperatures, with high CO selectivity and negligible side products. In this study, we investigate the synthesis of Cu/CeO₂ catalyst using Solution Combustion Synthesis (SCS) technique and its performance for the RWGS reaction using a tubular packed bed reactor. Results indicate that the catalytic activity and stability of CeO₂ at low and moderate temperatures can be effectively improved by the addition of a small quantity of copper (1 wt%). The conversion of CO₂ improves with an increase in temperature, with a maximum value of 70% at 600 °C, showing a steady time on stream (TOS) performance for 1200 min with negligible carbon deposition of <0.05 wt%. The high catalyst activity is due to the synergistic interaction between the active Cu⁰ species and Ce³⁺-oxygen vacancy. The Cu/CeO₂ catalyst was also found to have 100% selectivity for CO, and no CH₄ was detected in the outlet stream. Moreover, the morphological characteristics of the support and catalysts (fresh and post-reaction samples), as well as the impact of reaction on the catalysts surface were investigated using various methods such as x-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy with energy dispersive x-ray spectra (SEM/EDX). The results demonstrate that Cu/CeO₂ offers a good potential for being a robust RWGS catalyst with exclusive selectivity for CO without the undesired methanation side-reaction.     

Impacts of nickel loading on properties,catalytic behaviors of Ni/γ–Al2O3 catalysts and the reaction intermediates formed in methanation of CO2

In this study, methanation of CO₂ over Ni/Al₂O₃ with varied nickel loading (from 0 to 50 wt%) was evaluated, striving to explore the effects of nickel loading on catalytic behaviors and the reaction intermediates formed. The results showed that agglomeration of nickel particles were closely related to interaction between nickel and alumina. Increasing nickel loading resulted in the increased proportion of nickel having medium strong interaction with alumina, the reduced reduction degree of NiO, the increase of medium to strong basic sites, the enhanced activity for methanation and the competition between reverse water gas shift (RWGS) reaction and methanation. Lower nickel loading promoted RWGS reaction while methanation of CO₂ dominated at higher nickel loading. The catalyst with a nickel loading around 25% achieved the best activity for methanation. The in–situ DRIFTS studies of methanation of CO₂ showed that CO₂ could be absorbed on surface of metallic Ni, NiO or alumina. More metallic nickel species on alumina suppressed formation of carbonate species while promoted further conversion of HCOO¹ species and ¹CH₃ species, achieving a higher catalytic efficiency. Moreover, more metallic nickel species was crucial for gasifying the carbonaceous intermediates, prevented aggregation of the intermediates to coke and achieving a higher catalytic stability.     

The active phase of NaCo/ZnO catalyst for ethanol steam reforming: EXAFS and in situ XANES studies

The NaCo/ZnO catalyst was prepared by a co-precipitation method and the active phase for the catalyst was studied. Extended X-ray absorption fine structure (EXAFS) studies were used to obtain structural parameters of the active phase of the catalyst. In situ X-ray absorption near edge structure (XANES) studies were also employed to better understand the phase transition of the catalyst in the course of H₂-temperature-programmed reduction followed by ethanol steam reforming. The XANES analysis confirmed that the oxidic precursor of Co₃O₄ phase was transformed to CoO followed by Co metal in the course of H₂-TPR, and the Co metal phase remained stable during the reaction. The EXAFS analysis for the fresh and spent catalyst samples revealed that the characteristic features corresponding to Co–Co distance of Co metallic phase were being developed during reaction, which demonstrated that Co phase is most likely the active phase of NaCo/ZnO catalyst for the ethanol steam reforming. The catalytic activity in ethanol steam reforming for hydrogen production over the oxidized and reduced catalyst samples was measured at 773 K and 1 atm in a fixed bed reactor using a model liquid feed containing 21 vol% ethanol in water. The prereduced NaCo/ZnO catalyst gave high ethanol conversion of 99% with product distributions of 73.0% H₂, 2.2% CO, 22.1% CO₂, and 2.7% CH₄, while the calcined oxidic one exhibited poor ethanol conversion below 44% at 773 K.     

Alumina-supported cobalt catalysts in the hydrogenation of CO2 at atmospheric pressure

20 wt.% cobalt catalysts supported on pure and 5 wt.% silica-containing alumina have been prepared and characterized by X-Ray Diffraction, IR and DR-UV-vis-NIR spectroscopies and Field-Emission Scanning Electron Microscopy (FE-SEM). The presence of a cobalt-containing surface spinel phase Co_3-xAl_xO₄ and, for the silica-containing sample, of a segregated Co₃O₄ phase is evident. These catalysts have been tested in CO₂ hydrogenation at atmospheric pressure in steady state conditions in the temperature range 523–773 K. Both catalysts are active in CO₂ hydrogenation to methane (methanation) and to CO (reverse Water Gas Shift, rWGS). CO₂ hydrogenation activity is higher on freshly pre-reduced silica-free Co/Al₂O₃, while selectivity to methane is slightly higher on the silica-containing sample. Spent catalysts contain clustered or amorphous cobalt metal centers as active sites for methanation. The silica-containing catalyst shows slow deactivation in CO₂ hydrogenation upon 13 h experiments, with quite stable or even slightly increasing rWGS activity and decreasing CH₄ selectivity. This confirms previous data suggesting that, over cobalt catalysts, sites for methanation are metal centers prone to deactivation by carbon deposition. However, in contrast with what happens with unsupported and silica-supported cobalt catalysts, where deactivation is very fast, over these alumina-based catalysts carbon deposition and deactivation occur much more slowly. Sites for rWGS are unreduced cobalt centers which do not undergo such a deactivation phenomenon.     

Combustion synthesis of lanthanum oxide supported Cu,Ni, and CuNi nanoparticles for CO2 conversion reaction

The reverse water gas shift (RWGS) process is considered a feasible method for lowering greenhouse gas emissions by utilizing CO₂ and converting it to CO. Herein, we evaluated the catalytic conversion of CO₂ through the RWGS reaction over transition metal nanoparticles supported on lanthanum. Catalysts of selected active metals (Cu, Ni, and CuNi) on lanthanum oxide support were investigated in a packed bed tubular reactor within a temperature range of 100–600 °C to assess their catalytic activity and selectivity towards CO. The results of the catalyst's activity and stability experiments showed maximum CO₂ conversions of 57%, 68% and 74% for Cu–La₂O₃, Ni–La₂O₃, and CuNi–La₂O₃, respectively, at 600 °C and excellent stability over a 1440-min time on stream (TOS) with a carbon deposition rate of less than 3 wt%. However, among all investigated catalysts, only the 1 wt% Cu–La₂O₃ catalyst displayed a CO selectivity of 100% at all the studied temperatures, whereas the nickel-containing catalysts showed selectivity for methane along with carbon monoxide. Furthermore, the morphological properties of the support and catalysts, as well as the effect of the reaction conditions on the catalysts surface, were studied using a variety of techniques, including XRD, TEM, SEM-EDX and TPR. The results showed promising potential for the application of transition metal catalysts on lanthanum oxide support for RWGS that could be extended to other hydrogenation reactions.     

Experimental optimization analysis on operating conditions of CO removal process from hydrogen-rich reformate

The catalytic effects of CO preferential oxidation and methanation catalysts for deep CO removal under different operating conditions (temperature, space velocity, water content, etc.) are systematically studied from the aspects of CO content, CO selectivity, and hydrogen loss index. Results indicate that the 3 wt% Ru/Al₂O₃ preferential oxidation catalysts reduce CO content to below 10 ppm with a high hydrogen consumption of 11.6–15.7%. And methanation catalysts with 0.7 wt% Ru/Al₂O₃ also exhibit excellent CO removal performance at 220–240 °C without hydrogen loss. Besides, NiCl_x/CeO₂ methanation catalysts possess the characteristics of high space velocity, high activity, and high water-gas resistance, and can maintain the CO content at close to 20 ppm. Based on these experimental results, the coupling scheme of combining NiCl_x/CeO₂ methanation catalysts (low cost and high reaction space velocity) with 0.7 wt% Ru/Al₂O₃ methanation catalysts (high activity) to reduce CO content to below10 ppm is proposed.     

The influence of CO,CO2 and H2O on selective CO methanation over Ni(Cl)/CeO2 catalyst: On the way to formic acid derived CO-free hydrogen

For the first time the influence of CO, CO₂ and H₂O content on the performance of chlorinated NiCeO₂ catalyst in selective or preferential CO methanation was studied systematically. It was shown that the rate of CO methanation over Ni(Cl)/CeO₂ increases with the increasing H₂ concentration, is independent of CO₂ concentration and decreases with increasing CO and H₂O concentrations; the rate of CO₂ methanation is weakly sensitive to H₂ and CO₂ concentrations and decreases with increasing CO and H₂O concentrations. High catalyst selectivity was attributed to Ni surface blockage by strongly adsorbed CO molecules and ceria surface blockage by Cl, which both inhibit CO₂ hydrogenation.For the first time, selective CO methanation over Ni(Cl)/CeO₂ was studied for deep CO removal from formic acid derived hydrogen-rich gases characterized by high CO₂ (40–50 vol%), low CO (30–1000 ppm) content and trace amounts of water. Composite Ni(Cl)/CeO₂-η-Al₂O₃/FeCrAl wire mesh catalyst was demonstrated to be effective for this process at temperatures of 180–220°С, selectivity 30–70%, WHSV up to 200 L (STP)/(g∙h). The catalyst provides high process productivity, low pressure drop, uniform temperature distribution, and appears highly promising for the development of a compact CO cleanup reactor. Selective CO methanation was concluded to be a convenient way to CO-free hydrogen produced by formic acid decomposition.     

Metallic Ni nanocatalyst in situ formed from LaNi5H5 toward efficient CO2 methanation

LaNi₅ alloy can be utilized to directly store and release hydrogen in mild condition, thus it is considered as a long-term safe and stable solid-state hydrogen storage material. In this work, LaNi₅H₅ was used as the solid-state hydrogen source in the CO₂ methanation reaction. Impressively, the carbon dioxide conversion can be achieved to nearly 100% under 3 MPa mixed gas at 200 °C. The microstructure and composition analysis results reveal that the high catalytic activity may originate from the promoted elementary steps over in situ formed metallic Ni nanoparticles during the CO₂ methanation process. More importantly, as the lowered reaction temperature prevented the agglomeration of Ni nanoparticles, this catalyst exhibited durable stability with 99% conversion rate of CO₂ retained after 400 h cycling test.     

Carbon oxides methanation in equilibrium; a thermodynamic approach

Global warming and greenhouse gases as two main threat to human societies due to increasing carbon oxides, such as CO and CO₂ and lack of energy storages results in challenges efforts to controlling these atmospheric pollutions in various ways and methods. Carbon oxides methanation was considered as chemical process to conversion carbon oxides to their products as syngas. Various parameters can be effective on this process such as temperature, pressure and equivalence ratio of feeding products specially H₂/CO₂ and H₂/CO. In this study, three various equivalence ratio of feeding products were investigated against pressure and temperature in equilibrium condition to determine concentration of main products. Five various pressures applied to system of equilibrium, i.e. 1, 5, 10, 25, 50 atm beside temperature change from 200 K to 1500 K. Moreover, fugacity effects also were investigated in Soave–Redlich–Kwong equation of state in comparison with ideal gas. Results revealed that fugacity was completely changes the results especially for water production and hydrogen consumption. According to the results, carbon di and monoxides conversion were increased during pressure increasing where methane selectivity also increased. In maximum condition of coke formation there was 0.1 mol fraction of it in both CO and CO₂ methanation. Although, higher equivalence ratio of each carbon oxides combination feeding products ascended CH₄ selectivity and yield but in high equivalence ratio (ER = 6) CH₄ yield decreased about 8% for both investigated methanation process. In lower equivalence ratio (lower than stoichiometric) condition, methane yield replaced with mainly carbon yield.     

Enhanced CO hydrogenation performance via two-dimensional NiAl-layered double oxide decorated by SiO2 nanoparticles

The CO methanation reaction has been widely used in the fields of synthetic natural gas and ammonia (NH₃). This study improves the CO methanation performance using a two-dimensional NiAl-layered double oxide (2D NiAl-LDO) decorated by SiO₂ nanoparticles and reduced under hydrogen atmosphere. The as-obtained H–NiAl-LDO/SiO₂ exhibited a high specific surface area of 240.5 m²/g and high surface-adsorbed oxygen of 20.77%. Furthermore, it had an excellent CO conversion of 100% at 300 °C and 96.87% at 250 °C, which was much better than those of H–NiAl-LDO (84.03% at 300 °C and 0% at 250 °C). We believe that it provides an additional strategy to easily and effectively improve CO methanation performance and shows potential for the application of similar catalysts.     

Solid-state synthesis method for the preparation of cobalt doped Ni–Al2O3 mesoporous catalysts for CO2 methanation

In this study, a simple solid-state synthesis method was employed for the preparation of the Ni–Co–Al₂O₃ catalysts with various Co loadings, and the prepared catalysts were used in CO₂ methanation reaction. The results demonstrated that the incorporation of cobalt in nickel-based catalysts enhanced the activity of the catalyst. The results showed that the 15 wt%Ni-12.5 wt%Co–Al₂O₃ sample with a specific surface area of 129.96 m²/g possessed the highest catalytic performance in CO₂ methanation (76.2% CO₂ conversion and 96.39% CH₄ selectivity at 400 °C) and this catalyst presented high stability over 10 h time-on-stream. Also, CO methanation was investigated and the results showed a complete CO conversion at 300 °C.     

CO deep removal with a method of two-stage methanation

CO methanation experiments showed that it was difficult to reach both goals of CO removal depth of below 10 ppm and CO₂ conversion rate of below 5% by using a single catalyst in this paper. A two-stage methanation method by applying two kinds of catalysts is proposed, that is, one catalyst with relatively low activity and high selectivity for the first stage at higher temperatures, and another one with relatively high activity for the second stage at lower temperatures. CO can be removed from 1% to below 0.1% at the first stage and to below 10 ppm at the second stage with CO₂ conversion rate below 1% and below 4% at each stage respectively. In addition, results also showed that the reverse water-gas shift (RWGS) reaction at the second stage was the dominant factor of CO removal depth. Temperature programmed reduction (TPR) and H₂ chemisorption were applied to characterize the catalysts.     

Methanation reactions for chemical storage and purification of hydrogen: Overview and structure-reactivity correlations in supported metals

The drastic effects associated with climate changes, mainly induced by the increasing carbon emissions, challenge our modern society and mandate immediate solutions. This requires in the first place, accelerating the introduction of green alternatives for the standing carbon-based energy technologies, and simultaneously increasing the contribution of the carbon-free renewables to our energy sector. Among a few catalytic processes, the methanation of carbon oxides is currently envisaged as a cornerstone in the renewable energy concepts. On one hand, the methanation of CO is intensively studied for ultra-purification of reforming-generated hydrogen feed gases used in the low-temperature hydrogen fuel cells and in the production of ammonia. This involves the selective methanation of CO in CO₂-rich H₂ fuels to lower CO concentration from about 5000 ppm down to <5 ppm. The other major application involves the solo or the total methanation of CO and CO₂. This involves the conversion of syngas or the methanation of air-captured CO₂ using green hydrogen produced from renewable energies (power-to-gas). These aspects revive the importance of Sabatier reactions and presents them as an essential part of the cycle of renewable-energy applications. In this review, we will focus on the recent advancements of the methanation of CO and CO₂ on oxide supported Ni and Ru catalysts in the frame of their use in the abovementioned applications. After an overview of different catalytic processes related to hydrogen production, we will basically concentrate on the structure-reactivity relationships of CO and CO₂ methanation in different applications, highlighting limitations and advantages of different catalytic systems. Basically, we will map out the interplay of different electronic and structural features and correlate them to the catalytic performance for CO and CO₂ methanation. This includes the discussion of metal particle size effect, nature of the support, and the effect of reaction gas atmospheres. Clarifying the interplay of these parameters will help us to further understand the metal-support interaction (MSI) based on structural (SMSIs) and electronic (EMSIs) aspects which is essential for steering the catalytic performance of these catalysts for a specific reaction pathway.     

Cobalt-based nanoparticles as catalysts for low temperature hydrogen production by ethanol steam reforming

Results obtained in the synthesis, characterization and application as catalyst of cobalt nanoparticles are reported. Cobalt nanoparticles were prepared via reduction method in aqueous solution. Structural characterization was carried out using X-ray diffraction (XRD), morphological studies were performed with a scanning electron microscope equipped with a field emission gun (FE-SEM). A DC-superconducting quantum interference device “SQUID” magnetometer was used to measure the room temperature (RT) magnetic hysteresis cycle in the −5 ÷ 5 Tesla (T) μ₀H magnetic field range as well as magnetization as a function of temperature. This material is constituted by very small primary particles (∼2.8 nm radius) which appear amorphous to XRD and have a superparamagnetic behaviour. However, annealing at 773 K and also utilization in the catalytic reactor at the same temperature result in XRD detectable cubic Co nanocrystals. These unsupported cobalt nanoparticles were found catalytically active in the ethanol steam reforming reaction, producing hydrogen with 90% yield at 773 K. These nanoparticles show a better catalytic behaviour compared to those of more conventional Co and Ni based catalysts, due to very low CO and methane production, and with moderate formation of carbonaceous materials.     

Phosphate-modified Al2O3–ZrO2 supported Ni catalysts for efficient selective methanation of CO in H2-rich reformate gas

CO selective methanation can remove the CO in H₂-rich reformate gas to prevent the poisoning of Pt anode electrode in proton exchange membrane fuel cell. However, the methanation of CO₂ in H₂-rich gas consumes a lot of hydrogen, which greatly reduces the energy efficiency. In order to inhibit CO₂ methanation, mesostructured Al₂O₃–ZrO₂ was modified by different amounts of phosphate, and then was as Ni support. The structures and surface properties of Ni/Al₂O₃–ZrO₂ catalyst modified by phosphate were studied to reveal the effect of phosphate-modification on CO conversion and selectivity for CO methanation. It was found that the phosphate-modification inhibited the adsorption of CO₂, which increased the selective for CO methanation. But the modification with excess phosphate lessened active sites of Ni and weakened the adsorption of H₂ and CO, which decreased the activity of CO methanation.     

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.     

Low-temperature CO2 hydrogenation to CO on Ni-incorporated LaCoO3 perovskite catalysts

This work introduces LaCo_1-xNi_xO₃ (x = 0, 0.1, 0.25, and 0.4) perovskite catalysts for enhancing the low temperature performance of reverse water-gas shift (RWGS) reaction. Incorporating Ni lowers the interaction between La-site and B-site, weakening the electron donation from La-site to B-site. The B-site elements with the weak interaction can be easily diffused from the bulk to form exsolved bimetallic Co–Ni alloy on the surface. This different interaction trends further control H₂ dissociation activity and CO desorption that affect CO₂ conversion and CO selectivity, respectively. While the Ni-incorporated catalyst shows a higher metal dispersion to enhance H₂ dissociation activity and increases CO₂ conversion, the La-sites with the weak electron donation further drive the strong adsorption of CO molecules to be additionally hydrogenated, eventually lower CO selectivity. However, incorporating 10 at% Ni into the B site of LaCoO₃ (LaCo_0.9Ni_0.1O₃) achieved a balanced effect between facile H₂ dissociation and CO desorption to maximize RWGS activity. The LaCo_0.9Ni_0.1O₃ catalyst displayed outstanding activity with an average CO₂ conversion of 30.8%, which is close to the equilibrium conversion, and a CO selectivity of 98.8% at 475 °C over 50 h.     

Mesoporous zirconia-modified clays supported nickel catalysts for CO and CO2 methanation

The Ni catalysts supported on a new structure with zirconia nanoparticles highly dispersed on the partly damaged clay layers has been prepared by the incipient wetness impregnation method and the new structure of the support has been prepared in one pot by the hydrothermal treatment of the mixture of the clay suspension and the ZrO(NO₃)₂ solution. The catalytic performances for the CO and CO₂ methanation on the catalysts have been investigated at a temperature range from 300 °C to 500 °C at atmospheric pressure. The catalysts and supports have been characterized by X-ray diffraction (XRD), transmittance electron microscopy (TEM), H₂ temperature-programmed reduction (H₂-TPR), nitrogen adsorption–desorption, and thermogravimetry and differential thermal analysis (TG-DTA). It is found that the zirconia-modified clays have the typical bimodal pore size distribution. Most of the pores with the sizes smaller than 10 nm are resulted from the zirconia pillared clays and the mesopores with the sizes larger than 10 nm and the macropores with the sizes larger than 50 nm are resulted from the partly damaged clay layers. The bimodal pore structure is beneficial to the dispersion of Ni on the layers of the zirconia-modified clays and the increase in Ni loading. The zirconia nanoparticles are highly dispersed on the partly damaged clay layers. Nickel oxide in cubic phase is the only Ni species that can be detected by XRD. The nickel oxide nanoparticles with the sizes of 12 nanometers or more are well dispersed on the zirconia-modified clay layers, which are observed to be buried in the stack layers of zirconia. The presence of nickel oxide in six different forms could be perceived on the new structure. Five of them except the Ni species that forms the spinel phase with Al in clays can be reduced to the active Ni species for the CO and CO₂ methanation. But the activity of the Ni species is different, which is associated with the chemical environment at which the Ni species is located. The catalyst with the higher zirconia content, which also has the larger specific surface area and pore volume, exhibits the better catalytic performance for the CO or CO₂ methanation. Zirconia in the catalyst is responsible for the dispersion of the Ni species, and it prevents the metallic Ni nanoparticles from sintering during the process of the reaction. In addition, it is also responsible for the reduction of the inactive carbon deposition. The catalyst with 15 wt.% zirconia content has the highest CO conversion of about 100% and the highest methane selectivity of about 93% at 450 °C for CO methanation, and the catalyst with 20% zirconia content has the CO₂ conversion of about 80% and the highest methane selectivity of about 99% for CO₂ methanation at 350 °C. The catalyst with 15 wt.% zirconia possesses promising stability and no distinct deactivation could be perceived after reaction for 40 h. This new catalyst has great potential to be used in the conversion of the blast furnace gas (BFG) and the coke oven gas (COG) to methane.     

Ni and Co-based catalysts supported on ITQ-6 zeolite for hydrogen production by steam reforming of ethanol

Ni and Co catalysts supported on ITQ-6 zeolite have been synthesized and evaluated in the steam reforming of ethanol (SRE). Catalysts were also characterized by means of N₂ adsorption-desorption, XRD, H₂-TPR, and H₂-chemisorption. ITQ-6 containing Co (Co/ITQ-6) presented a higher conversion of ethanol and production of hydrogen than ITQ-6 containing Ni (Ni/ITQ-6). The lower size of the metallic cobalt particles shown in Co/ITQ-6 seems to be the major responsible of its higher catalytic performance. Regarding the reaction by-products (CO, CH₄, C₂H₄O and CO₂), Co/ITQ-6 showed the lowest selectivity at medium and high temperatures (773 and 873 K). At low reaction temperatures (673 K) the dehydrogenation reaction predominates in the Co/ITQ-6, what it is supported by the high concentration of acetaldehyde detected at this temperature. In the case of the Ni/ITQ-6 the main side reaction at 673 K seems to be the methanation reaction since large concentrations of methane are detected. Stability studies were also carried out showing lower deactivation of Co/ITQ-6 at large reaction times (24 h). Characterization of the exhausted catalysts after reaction showed the presence of coke in both catalysts. Nevertheless, Co/ITQ-6 presented the lowest coke deposition. In addition, Co/ITQ-6 exhibited the lowest metal sinterization, what could be also account for the lower deactivation exhibited by this sample. This fact could be related to the higher interaction between the cobalt metallic particles and the ITQ-6 support as the H₂-TPR studies demonstrate.     

Promoted Ni–Co–Al2O3 nanostructured catalysts for CO2 methanation

15 wt.%Ni-12.5 wt.%Co–Al₂O₃ catalysts promoted with Fe, Mn, Cu, Zr, La, Ce, and Ba were prepared by a novel solid-state synthesis method and employed in CO₂ methanation reaction. BET, XRD, EDS, SEM, TPR, TGA, and FTIR analyses were conducted to identify the chemicophysical characteristics of the prepared samples. The addition of Fe, Mn, La, Ce, and Ba was effective to improve the catalytic performance of the 15 wt%Ni-12.5 wt%Co–Al₂O₃ due to the higher CO₂ adsorption capacity of the promoted catalysts. Among the studied promoters, the Fe-promoted catalyst possessed the highest catalytic activity (X_CO2 = 61.2% and S_CH4 = 98.87% at 300 °C). Also, the effect of calcination temperature, feed composition, and GHSV on the performance of the 15 wt%Ni-12.5 wt%Co-5wt%Fe–Al₂O₃ catalyst in CO₂ methanation reaction was assessed. The outcomes confirmed that the 15 wt%Ni-12.5 wt%Co-5wt%Fe–Al₂O₃ catalyst with the BET area of 122.4 m²/g and the highest pore volume and largest pore diameter had the highest catalytic activity. Also, the catalytic performance in the methanation of carbon monoxide was studied, and 100% conversion of carbon monoxide was observed at 250 °C.