Dry reforming of methane over silica zeolite-encapsulated Ni-based catalysts: Effect of preparation method,support structure and Ni content on catalytic performance

Dry reforming of methane (DRM) is a prospective technology for efficient utilization of CH₄ and CO₂, with the essential challenge being the design and synthesis of efficient catalysts. In this research, serial encapsulated Ni-based catalysts (xNi@S-1, x = 5, 7, 10) by silica zeolite (S-1) were prepared successfully. The effects of support structure, preparation method and Ni content upon the catalytic performance for DRM were investigated and diverse characterizations were utilized for revealing structural features of as-prepared catalysts. Encapsulated 7Ni@S-1 catalyst prepared using the one-pot hydrothermal method could acquire more homogeneously dispersed metallic Ni particles and more Ni species including Ni⁰, NiO, 1:1/2:1 Ni phyllosilicates that could facilitate forming stable Ni⁰ sites and Ni²⁺-O^2- ion pairs for adsorption and activation of CH₄ and CO₂, respectively. Hence, 7Ni@S-1 still maintained the highest CH₄ and CO₂ conversions of 57.9% and 88.6% and H₂/CO molar ratio of 0.90 after 52 h stability tests.     

Carbon dioxide methanation over Ni catalysts prepared by reduction of NixMg3‒xAl hydrotalcite-like compounds: Influence of Ni:Mg molar ratio

A series of supported Ni catalysts have been prepared from Ni_xMg_3?xAl hydrotalcite-like compounds (HTlcs) and the influence of Ni:Mg molar ratio on the structural property and catalytic activity for CO₂ methanation is investigated. The catalysts were characterized by N₂ physical adsorption, X-ray powder diffraction (XRD), temperature-programmed reduction (H₂-TPR), temperature-programmed desorption (CO₂-TPD), H₂ chemisorption, scanning electronic microscopy (SEM), scanning transmission electronic microscopy (STEM), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). By reducing HTlcs at 800 °C, well dispersed Ni particles with average size of 5–10 nm are formed. The Ni crystal size decreases with the decrease of Ni:Mg ratio, attributable to the strong interaction between nickel and magnesium oxides. Among the catalysts, Ni₂Mg₁Al-HT shows the highest activity, giving ～93% CO₂ conversion and >99% CH₄ selectivity at 275 °C and SV = 5000 mL g^?1 h^?1. Meanwhile, this catalyst exhibits good stability without obvious sintering and coking. The high activity is related to the large amount of surface Ni⁰ species and medium basic sites. From CO₂-TPD and DRIFTS, it is inferred that CO₂ adsorbs on the medium basic sites, i.e., Ni–Mg(Al)O interface, forming monodentate carbonate. In situ DRIFTS reveals that monodentate carbonate, monodentate formate, and adsorbed CO are the main intermediate species, suggesting that the reaction may proceed via the formate formation route.     

Theoretical investigation of the reactivity of flat Ni (111) and stepped Ni (211) surfaces for acetic acid hydrogenation to ethanol

Reactivity of two types of Ni surfaces-flat (111) and stepped (211) surfaces for acetic acid hydrogenation to ethanol was investigated using density functional theory method. The most stable configurations of the reactants, intermediates and products were obtained by investigating all the possible adsorption sites. Results showed that the adsorption of all the studied molecules on the Ni (211) surface are stronger than that on the Ni (111) surface, except for H atom (similar adsorption strength of H atom on the both surfaces was found). In addition, most of the molecules on the Ni (211) surface preferred to adsorb at the step edge, indicating that different coordination numbers of Ni atoms could result in different adsorption strength. Moreover, the elementary reactions with energy barriers related to ethanol and ethyl acetate formations were studied. The most favorable pathways for ethanol formation on the Ni (111) and (211) surfaces are CH₃COOH → CH₃CO → CH₃CHO → CH₃CHOH→ CH3CH₂OH and CH₃COOH → CH₃CO → CH₃COH → CH₃CHOH → CH₃CH₂OH, respectively. The direct decomposition of acetic acid molecule to form acetyl species was the rate-determining step on the both surfaces. Slight difference for the rate-determining step barriers was observed (1.04 eV vs. 1.13 eV). However, the elementary step of ethyl acetate formation by CH₃CO and CH₃CH₂O became much more difficult on the Ni (211) surface than that on the Ni (111) surface (1.06 eV vs. 0.67 eV). These results suggests that the Ni (211) surface is more likely to inhibit ethyl acetate formation compared with the Ni (111) surface. Meanwhile, the results of the rate constants and the effective barriers indicates that the Ni (211) surface presents a higher probability for higher ethanol selectivity.     

Hydrogen production via steam reforming of coke oven gas enhanced by steel slag-derived CaO

Steel slag, a waste from steelmaking plant, has been proven to be good candidate resources for low-cost calcium-based CO₂ sorbent derivation. In this work, a cheap and sintering-resistance CaO-based sorbent (CaO (SS)) was prepared from low cost waste steel slag and was applied to enhance catalytic steam reforming of coke oven gas for production of high-purity hydrogen. This steel slag-derived CaO possessed a high and stable CO₂ capture capacity of about 0.48 g CO₂/g sorbent after 35 adsorption/desorption cycles, which was mainly ascribed to the mesoporous structure and the presence of MgO and Fe₂O₃. Product gas containing 95.8 vol% H₂ and 1.4 vol% CO, with a CH₄ conversion of 91.3% was achieved at 600 °C by steam reforming of COG enhanced by CaO (SS). Although high temperature was beneficial for methane conversion, CH₄ conversion was remarkably increased at lower operation temperatures with the promotion effects from CaO (SS), and CO selectivity has been also greatly decreased. Reducing WHSV could increase methane conversion and reduce CO selectivity due to longer reactants residence time. Reducing C/A could increase methane conversion and hydrogen recovery factor, and also decrease CO selectivity. When being mixed with catalyst during SE-SRCOG, CaO (SS) with a uniform size distribution favored methane conversion due to the high utilization efficiency of catalyst. Promising stability of CaO (SS) in cyclic reforming/calcination tests was evidenced with a hydrogen recovery factor >2.1 and CH₄ conversion of 82.5% at 600 °C after 10 cycles using CaO (SS) as sorbent.     

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.     

Ni/CeO2 catalysts with high CO2 methanation activity and high CH4 selectivity at low temperatures

CO₂ methanation was performed over 10 wt%Ni/CeO₂, 10 wt%Ni/α-Al₂O₃, 10 wt%Ni/TiO₂, and 10 wt%Ni/MgO, and the effect of support materials on CO₂ conversion and CH₄ selectivity was examined. Catalysts were prepared by a wet impregnation method, and characterized by BET, XRD, H₂-TPR and CO₂-TPD. Ni/CeO₂ showed high CO₂ conversion especially at low temperatures compared to Ni/α-Al₂O₃, and the selectivity to CH₄ was very close to 1. The surface coverage by CO₂-derived species on CeO₂ surface and the partial reduction of CeO₂ surface could result in the high CO₂ conversion over Ni/CeO₂. In addition, superior CO methanation activity over Ni/CeO₂ led to the high CH₄ selectivity.     

Three-dimensional porous Mn–Ni/Al2O3 microspheres for enhanced low temperature CO hydrogenation to produce methane

CO methanation has attracted much attention because it transforms CO in syngas and coke oven gas into CH₄. Here, porous Al₂O₃ microspheres were successfully used as catalyst supports meanwhile the Mn was used as a promoter of Ni/Al₂O₃ catalysts. The as-obtained Ni/Al₂O₃ and Mn–Ni/Al₂O₃ samples display a micro-spherical morphology with a center diameter near 10 μm. Versus the Ni/Al₂O₃ catalyst, the 10Mn–Ni/Al₂O₃ catalyst exhibits a high specific surface area of 92.5 m²/g with an average pore size of 7.0 nm. The 10Mn–Ni/Al₂O₃ catalyst has the best performance along with can achieve a CO conversion of 100% and a CH₄ selectivity of 90.7% at 300 °C. Even at 130 °C, the 10Mn–Ni/Al₂O₃ catalyst shows a CO conversion of 44.0% and a CH₄ selectivity of 84.1%. The higher low-temperature catalytic activity may be since the catalyst surface contains more CO adsorption sites and thus has a stronger adsorption performance for CO. Density functional theory (DFT) calculations confirm that the Mn additive enhances the adsorption of CO, especially for the 10Mn–Ni/Al₂O₃ catalyst with the strongest adsorption energy.     

Trace metals supplementation enhanced microbiota and biohythane production by two-stage thermophilic fermentation

The effect of trace metals supplementation into palm oil mill effluent on biohythane production and responsible microbial communities in thermophilic two-stage anaerobic fermentation was investigated. High biohythane yields were linked to Ni/Co/Fe supplementation (10, 6 and 20 mg L⁻¹, respectively) with maximum H₂ and CH₄ yields of 139 mL H₂ gVS⁻¹ and 454 mL CH₄ gVS⁻¹, respectively. The Ni/Co/Fe supplementation resulted in higher numbers of Bacillus sp., Clostridium sp. and Thermoanaerobacterium sp. together with increasing hydrogenase expression level leading to increasing hydrogen yields of 90.4%. The numbers of Methanosarcina, Methanomassiliicoccus, and Methanoculleus were enhanced by Ni/Co/Fe addition, accompanied by 21.7% higher methane yields. No correlation between methyl coenzyme-M reductase expression level and methane yields was observed. The Ni/Co/Fe supplementation improved gas production in the two-stage biohythane process via enhancing a number of viable hydrogen-producing bacteria together with hydrogenase activity in H₂ stage and enhancing number methanogens in the CH₄ stage.     

Molecular transition metal corrole as an efficient electrocatalyst for the heterogeneous CO2 electroreduction: A theory study

Carbon dioxide electrochemical reduction (eCO₂RR) has been regarded as an important solution for low-carbon economy. However, challenges remain for searching low-cost and high selectivity catalysts. Here, we investigated electrocatalytic activity of molecular catalysts containing transition metal single atom supported on corrole as the eCO₂RR catalysts (TM/SACC) by DFT. Various C₁ products can be produced on the 14 TM/SACC, including methane (CH₄), formic acid (HCOOH) and CO. We found CO and formic acid are major products on TM/SACC (TM = Ni, Pd, Zn, Cu, Au, Ag) at higher overpotentials, while methane are major eCO₂RR products on TM/SACC (TM = Mn, Cr, Nb, Mo, Zr, V, Ti, Cd) at lower overpotentials. Our studies indicate Mn/SACC gives high selectivity for methane formation. Due to the lowest overpotential value of 0.46 V, Mn/SACC can be a quite promising catalyst with excellent performance for reduction of CO₂ to methane along the most favorable pathway: CO₂ → COOH1 → CO1 → CHO1 → CH₂O1 → CH₂OH1 → CH₃OH1→CH₃1→CH₄1→CH₄(g), among which the hydrogenation of CHO1 to CH₂O1 and CH₃OH1 to CH₃1 and H₂O are the limiting-potential step and rate-determining step, respectively. The study shows corrole with different transition metal could adjust the catalytic performance of electrocatalysts, which offer a hopeful strategy for the design of molecular catalysts.     

Single-phase Ni3Sn alloy alkali-leached for hydrogen production from methanol decomposition

Methanol decomposition over alkali-leached Ni₃Sn powder at 513–793 K was investigated. Compared with untreated Ni₃Sn, alkali-leached Ni₃Sn had high catalytic activity and selectivity toward H₂ and CO production above 633 K. A maximum H₂ production rate of 100 × 10⁻³ mol h⁻¹ g-Cat⁻¹ and H₂ selectivity above 95% were attained over alkali-leached Ni₃Sn at 793 K. Alkali-leached Ni₃Sn presented good catalytic activity for 45 h of reaction at 713 K, whereas Ni₃Sn had none. The activation energy was calculated, and its values rapidly decreased from Ni₃Sn to alkali-leached ones. The improvement was attributed to the formation of Ni nanoparticles less than 100 nm in diameter in the alkali-leaching process, which had high activity for methanol decomposition. The improved catalytic activity favored the gradual formation of fine Ni₃Sn particle during the reaction, which served as the active sites for methanol decomposition when the catalytic activity decreased because of carbon deposition on the Ni surface. Results demonstrated that alkali-leached Ni₃Sn was a promising potential catalyst for hydrogen production from methanol.     

Effective encapsulation of Ni nanoparticles in metal-organic frameworks and their application for CO2 methanation

Ni(10 wt%)@UiO-66 and Ni(10 wt%)@MIL-101 composites were prepared by the classical impregnation method (IMP) and the “double solvent method” (DS), followed by the rapid and simple reduction of Ni²⁺ to Ni⁰ by aqueous solution of NaBH₄. Structural characterization by BET, XRD, TGA, SEM/EDX, EELS, XPS showed that Ni nanoparticles of maximum 4 nm are uniformly dispersed on the microporous UiO-66 or the mesoporous MIL-101 support, regardless of the deposition method, without any significant difference in crystallinity and morphology of the MOF support. Functional characterization through temperature programmed desorption of CO₂ (CO₂-TPD) reveals an important contribution of the Ni-MOF interaction in the CO₂ adsorption capacity. The best catalytic performance in CO₂ hydrogenation reaction was obtained in case of the Ni@MIL-101 (IMP) sample: X_CO2 of 56.4%, and S_CH4 of 91.6% at 320 °C, 4650 h⁻¹ and CO₂:H₂ = 1:8. All catalyst samples show stable catalytic performance parameters over a 10 h time on stream.     

Doping Fe and Zn to modulate Ni nanoparticles on IM-5 for methane decomposition to form hydrogen and CNTs

Catalysts Ni/IM-5 doped with Fe and/or Zn were studied to promote the performance in the catalytic decomposition of methane (CDM) to simultaneously produce hydrogen and carbon nanotubes (CNTs). The catalyst Ni₂₀Fe₅Zn₅/IM-5 showed high methane conversion (c.a. 65%) and 100% selectivity towards H₂ in 300 min at 670 °C. In the Fe atoms inhibited the formation of larger Ni particles. Zn atoms enhanced the migration of C atoms over the surface of the catalyst. IM-5 was speculated to provide better diffusion of C atoms to avoid the excessive deposition of carbon. The synergistic effect between metal and IM-5 enabled the catalyst to selectively produce pure and high graphitization CNTs. A carbon migration model was proposed to explain the synergistic effect between metals and zeolite. The atom erosion as dominant reason of catalyst deactivation was confirmed by XRD and TEM. According to density functional theory (DFT), bimetallic Fe and Zn promoter catalyst was more favorable for the initial bond cleavage of CH₄.     

The CO removal performances of Cr-free Fe/Ni catalysts for high temperature WGSR under LNG reformate condition without additional steam

The goal of this study was to investigate Cr-free, Fe/Ni, metal oxide catalysts for the high temperature shift (HTS) reaction of a fuel processor using liquefied natural gas (LNG). As hexavalent chromium (Cr⁶⁺) in commercial HTS catalyst is a hazardous material, we selected Ni as a substitute for chromium in the Fe-based HTS catalyst and investigated the HTS activities of these Cr-free, metal oxide catalysts under the LNG reformate condition. Cr-free, Fe/Ni-based catalysts containing Ni instead of Cr were prepared by coprecipitation and their performance was evaluated under a gas mixture condition (56.7% H₂, 10% CO, 26.7% H₂O, and 6.7% CO₂) that simulated the gas composition from a steam methane reformer (SMR, at H₂O/CH₄ ratio = 3 with 100% CH₄ conversion). Under this condition, the Fe/Ni catalysts showed higher CO removal activities than Fe-only and Cr-containing catalysts, but the methanation was promoted when the Ni content in the catalyst exceeded 50 wt%. Brunner-Emmett-Teller (BET), X-ray diffraction (XRD), inductively coupled plasma (ICP) and X-ray photoelectron spectroscopy (XPS) analyses were performed to explain the HTS activity of the Fe/Ni catalysts based on the catalyst structure.     

Carbon resistance of xNi/HTASAO5 catalyst for the production of H2 via CO2 reforming of methane

xNi/HTASAO5 catalysts (x = 2.5, 3.3, 4.4, 5.8, 8.2) were prepared for CO₂ reforming of methane. No crystalline nickel species formed on the catalysts with lower nickel content (≤4.4%), and large Ni⁰ crystallite formed on 5.8% (10 nm) and 8.2 wt%Ni/HTASAO5 (17 nm), whereas the surface concentration of Ce³⁺ decreased with Ni loading. The initial conversion of CH₄ increased from 29.5% to 46.9% with Ni loading. The xNi/HTASAO5 (x ≤ 4.4%) performed stably in the reaction due to the presence of dispersed Ni species and high surface Ce³⁺ content without coke formation, however, 5.8% and 8.2 wt%Ni/HTASAO5 exhibited decreased activity with time on stream, because of the formation of large Ni particles with lower surface Ce³⁺, leading to carbon accumulation. Thus, CH₄ conversion stabilized at about 43% and no carbon formed on 4.4 wt%Ni/HTASAO5 with optimum Ni loading.     

Plasma-assisted CO2 reforming of methane over Ni-based catalysts: Promoting role of Ag and Sn secondary metals

Carbon dioxide (CO₂) and methane (CH₄) are the primary greenhouse gases (GHGs) that drive global climate change. CO₂ reforming of CH₄ or dry reforming of CH₄ (DRM) is used for the simultaneous conversion of CO₂ and CH₄ into syngas and higher hydrocarbons. In this study, DRM was investigated using Ag–Ni/Al₂O₃ packing and Sn–Ni/Al₂O₃ packing in a parallel plate dielectric barrier discharge (DBD) reactor. The performance of the DBD reactor was significantly enhanced when applying Ag–Ni/Al₂O₃ and Sn–Ni/Al₂O₃ due to the relatively high electrical conductivity of Ag and Sn as well as their anti-coke performances. Using Ag–Ni/Al₂O₃ consisting of 1.5 wt% Ag and 5 wt% Ni/Al₂O₃ as the catalyst in the DBD reactor, 19% CH₄ conversion, 21% CO₂ conversion, 60% H₂ selectivity, 81% CO selectivity, energy efficiency of 7.9% and 0.74% (by mole) coke formation were achieved. In addition, using Sn–Ni/Al₂O₃, consisting of 0.5 wt% Sn and 5 wt% Ni/Al₂O₃, 15% CH₄ conversion, 19% CO₂ conversion, 64% H₂ selectivity, 70% CO selectivity, energy efficiency of 6.0%, and 2.1% (by mole) coke formation were achieved. Sn enhanced the reactant conversions and energy efficiency, and resulted in a reduction in coke formation; these results are comparable to that achieved when using the noble metal Ag. The decrease in the formation of coke could be correlated to the increase in the CO selectivity of the catalyst. Good dispersion of the secondary metals on Ni was found to be an important factor for the observed increases in the catalyst surface area and catalytic activities. Furthermore, the stability of the catalytic reactions was investigated for 1800 min over the 0.5 wt% Ag-5 wt% Ni/Al₂O₃ and 0.5 wt% Sn-5 wt% Ni/Al₂O₃ catalysts. The results showed an increase in the reactant conversions with an increase in the reaction time.     

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.     

Vanadium promoted Ni(Mg,Al)O hydrotalcite-derived catalysts for CO2 methanation

A series of V-promoted hydrotalcite-derived nickel catalysts (1.0, 2.0, and 4.0 wt%) were tested in CO₂ methanation. Ni–I–V2.0 with 2.0 wt% vanadium loading showed the highest catalytic activity, achieving 74.7% of CO₂ conversion and 100% of CH₄ selectivity at 300 °C. XRD and XANES analyses showed that the smallest Ni⁰ particles in Ni–I–V2.0 were consistent with the improved textural features observed for this catalyst. Moreover, CO₂-TPD revealed the highest sum of weak and medium basic sites in Ni–I–V2.0 that can positively influence catalytic behavior. For the studied catalysts, a clear correlation was demonstrated between the catalytic activity and specific surface area, as well as the basic properties.     

Catalytic performance of Ni–Al nanoparticles fabricated by arc plasma evaporation for methanol decomposition

The catalytic properties of Ni-25 at% Al (Ni25Al) nanoparticles fabricated by arc plasma evaporation toward methanol decomposition were studied at temperatures ranging from 513 to 753 K. The Ni25Al nanoparticles showed much higher activity than gas atomized Ni25Al powders. They showed a high degree of selectivity for methanol decomposition into H₂ and CO. Side reactions such as methanation and water-gas shift reaction were suppressed to a high temperature of 673 K, which is hardly achieved for common Ni catalysts. Detailed characterization of the Ni25Al nanoparticles showed that they were composed of Ni, Ni₃Al, and Al₂O₃ phases with Ni and Al oxides on the surface of the Ni and Ni₃Al phases. The Ni oxides were reduced to Ni phase by a hydrogen reduction prior to methanol decomposition, while the Al oxides remained unchanged. It is supposed that the Ni phase provided the active sites for methanol decomposition, and the Ni₃Al and Al₂O₃ phases acted as supports for the Ni phase. Probably the Ni₃Al and Al₂O₃ phases provided good resistance to agglomeration of the Ni phase during the reaction, which might contribute to maintain the high catalytic performance of the nanoparticles for methanol decomposition.     

Enhanced photocatalytic hydrogen evolution and CO2 to CH4 selectivity of Co3O4/Ti3+-TiO2 hollow S-scheme heterojunction via ZIF-67 self-template and Ti3+/Ov

The potential would be an important issue for enhancing photocatalytic HER and CO₂ photoreduction selectivity. Herein, the Co₃O₄/Ti³⁺-TiO₂ hollow S-scheme heterojunction is fabricated via continuous light modification-chemical-annealing-reduction method. Evaluated by photocatalytic performance, the as-prepared Co₃O₄/Ti³⁺-TiO₂ hollow S-scheme heterojunction exhibits remarkable photocatalytic performance enhancement than single TiO₂, including hydrogen evolution (∼396.16 μmol/g·h, ∼15 folds) and CO₂ photoreduction (H₂/CH₄/CO: ∼20.32/80.57/9.85 μmol/g·h, ∼20 folds), and achieves CO₂ photoreduction to CH₄ selectivity enhancement, which can be mainly ascribed to the synergism of Ti³⁺/O_v and S-scheme heterojunction. There, Ti³⁺/O_v can not only increase the solar efficiency, but also decrease the energy barrier of H⁺ and 1CO photoreduction to enhance HER and CO₂ to CH₄ selectivity, including promote the H⁺ diffusion and CO₂ absorption. Additionally, the formed Co₃O₄/Ti³⁺-TiO₂ S-scheme heterojunction can promote the photo-generated carrier separation/transportation. Also, the hollow 3D structure obtained by ZIF-67 self-template can increase solar efficiency and stability.     

High temperature methanation over Ni catalysts supported on high surface area ZnxMg1-xAl2O4: Influence on Zn loading

A series of 10 wt % Ni based catalysts supported on Zn_xMg_1-xAl₂O₄ were prepared using a co-precipitation and impregnation method for high temperature syngas methanation. The effect of Zn loading on catalysts’ textural property and catalytic performance was investigated by BET, XRD, TEM, H₂-TPR, XPS and CO-TPD analysis. It was found that a modest addition of Zn significantly increased the surface area of the catalysts, which moderated the strong interaction between NiO and the support. This effect enhanced the reduction of the Ni, thereby improving the dispersion of the active metal on the support and intensifying the adsorption of CO. In addition, surface Ni⁰ concentration was improved by the Zn substitution. Among the various catalysts tested, Ni/Zn_0.7Mg_0.3Al exhibited the best catalytic performance at 500 °C, 2.0 MPa and 30, 000 ml g⁻¹·min⁻¹, with a CO conversion, CO₂ conversion and CH₄ selectivity of 99.7, 53.1 and 98.7%, respectively. Furthermore, the Ni/Zn_0.7Mg_0.3Al catalysts also maintained excellent stability during a 120 h life test.