Thermo-catalytic conversion of greenhouse gases (CO2 and CH4) to CO-rich hydrogen by CeO2 modified calcium iron oxide supported nickel catalyst

In this study, the thermo-catalytic conversion of two principal greenhouse gases (methane and carbon dioxide) to carbon monoxide (CO)-rich hydrogen (H₂) is investigated over cerium oxide (CeO₂) promoted calcium ferrite supported nickel (Ni/CaFe₂O₄) catalyst. The CeO₂ promoted Ni/CaFe₂O₄ catalyst was prepared using wet-impregnation technique. To ascertain the physicochemical properties, the as-prepared catalyst was characterized using various instrument techniques. The characterization of the catalysts reveals that CeO₂-Ni/CaFe₂O₄ possesses suitable physicochemical properties for the conversion of methane (CH₄) and carbon dioxide (CO₂) to CO-rich H₂. The thermo-catalytic reaction revealed that the CeO₂ promoted Ni/CaFe₂O₄ catalyst displayed a higher CH₄ and CO₂ conversions of 90.04% and 91.2%, respectively, at a temperature of 1073 K compared to the unpromoted catalyst. The highest H₂ and CO yields of 78% and 76%, respectively, were obtained over the CeO₂-Ni/CaFe₂O₄ at 1073 K and CH₄/CO₂ ratio of 1. The CeO₂ promoted Ni/CaFe₂O₄ catalyst remained stable throughout the 30 hours time on stream (TOS) while that of the unpromoted Ni/CaFe₂O₄ catalyst sharply decreased after 22 hours TOS. The characterization of the used catalysts confirms the evidence of carbon depositions on the unpromoted Ni/CaFe₂O₄ which is solely responsible for its deactivation. Whereas, there was a slightly gasifiable carbon deposited on the CeO₂ promoted Ni/CaFe₂O₄ catalyst which could be ascribed to the interaction effect of the CeO₂ promoter on the Ni/CaFe₂O₄ catalyst.     

Catalytic CO2 reforming of CH4 over MgAl2O4 supported Ni-Co catalysts for the syngas production

Ni, Co and Ni–Co bimetallic catalysts of different ratios were synthesized by the Incipient Wetness Impregnation Method (IWI) over Magnesium Aluminate support, keeping the total metal loading 15 wt.%, characterized and tested for the reforming of methane with carbon dioxide at 873 K and 1 atm pressure. Magnesium Aluminate supported catalysts were also compared with Al₂O₃ supported Ni catalysts with similar metal loading. The results obtained revealed that MgAl₂O₄ exhibited excellent thermal stability as compared to Al₂O₃ as support at higher temperatures. Ni–Co catalyst, with an explicit Ni:Co (3:1) ratio for the 75Ni25Co/MgAl₂O₄ provided the highest CH₄ conversion and was about 1.82 times that of the 100Ni/MgAl₂O₄; CO₂ conversion also followed similar trends. Co-existence of Ni and Co with synergic effect in an explicit Ni:Co (3:1) ratio reduced the reduction temperature and increased the amount of metal in 75Ni25Co/MgAl₂O₄. CH₄ and CO₂ conversions, TOF_DRM, H₂: CO ratios and catalyst deactivations were related to the concentrations of the Ni–Co and particularly an explicit ratio of 3:1 for the Ni:Co in 75Ni25Co/MgAl₂O₄ catalyst provided the best initial & final conversions, TOF_DRM and H₂:CO ratio. Detail carbon analysis suggested that the type of coke deposited on 75Ni25Co/MgAl₂O₄ after the DRM reaction is of the same nature and are originating from the CH₄ cracking reaction and are of reactive type.     

Preparation and improvement of the mesoporous nanostructured nickel catalysts supported on magnesium aluminate for syngas production by glycerol dry reforming

Dry reforming of glycerol is an interesting method for syngas production due to its H₂/CO ≈ 1 that is suitable for FT synthesis. In this study, the performance of the Ni/MgO.Al₂O₃ catalysts with different nickel contents was investigated in glycerol dry reforming. The MgO.Al₂O₃ carrier was prepared by a simple sol-gel method and the nickel-based catalysts were synthesized by the wet impregnation method. The prepared catalysts possessed high BET surface area and pore volume. The TPR analysis showed a strong interaction between Ni and the catalyst support. The results demonstrated that the glycerol conversion decreased by increasing in CO₂/glycerol (GRR) molar ratio. All the prepared samples showed high stability in glycerol dry reforming during 25 h of reaction, indicating the high resistance of the catalysts against carbon formation. Also, 10 wt%Ni/MgO.Al₂O₃ catalysts possessed the highest catalytic performance (52% of glycerol conversion at 750 °C) due to the high dispersion of nickel on the prepared carrier.     

Low-temperature CO2 reforming of methane over Ni supported on ZnAl mixed metal oxides

Ni catalysts supported on mixed ZnOAl₂O₃ and on pure ZnO and Al₂O₃ were prepared, characterized by XRD, TPR, and XPS, and tested in long-term methane dry reforming at low temperature (400 °C). Depending on Zn/Al ratio in the supports, the catalysts varied in their physico-chemical properties and exhibited different trends in their on-stream catalytic activity. Catalysts with high alumina content consist of a mixture of alumina and zinc aluminate phases with metallic Ni particles on their surface. These samples show medium activity for reforming and high on-stream stability. The catalysts on mixed Zn-rich supports were more active than those on Al-rich supports and exhibited maxima in their activity after 30–40 h on stream, while Ni on pure ZnO possessed very low activity. Such contrast in performance of Zn-rich catalysts was explained by detected transformation of initially formed NiZn alloy to a mixture of Ni and Ni₃ZnC_0.7 particles that are assumed to have higher activity for reforming. Moreover, the size of Ni-containing particles on Zn-rich supports decreased under reaction conditions resulting in higher Ni dispersion.     

Parametric study of catalytic dry reforming of methane for syngas production at elevated pressures

This study examined and elucidated the catalytic dry reforming of methane (DRM) for synthesis gas (syngas) production. The DRM performance was characterized using CH₄ and CO₂ conversions and product yields under various operating conditions and reactant compositions. A fixed-bed tubular reactor was used as the physical model and axisymmetric non-isothermal governing equations for the gas flow, energy transfer and species transport were solved numerically. The reactant inlet temperature was used as the primary parameter. Good agreement between the numerically predicted and experimentally measured data was obtained as the carbon formation reactions were included. A carbon-free reaction was obtained from the numerical model at high temperature which agreed with the thermodynamic equilibrium analysis. It was found that the DRM performance was degraded as the reaction pressure and reactant flow rate were increased. Under these conditions, carbon yield increases with the increase in pressure and reactant flow rate. It was also found that DRM performance can be enhanced by introducing excessive CO₂ into the reaction system. Carbon formation was suppressed by the excessive CO₂ supply. The numerical results also indicated that decreases in CO₂ and CH₄ partial pressures led to enhance the DRM performance. The addition of H₂ as one of the reactants suppresses CH₄ conversion and inhibited carbon formation while the addition of CO resulted in suppressing CO₂ conversion and enhancing carbon formation.     

Zeolite and clay based catalysts for CO2 reforming of methane to syngas: A review

The development of coke and heat resistant catalyst for dry reforming of methane (DRM) is the major bottleneck towards the industrialization and commercialization of the process. Zeolite-based and clay-based catalysts are promising candidates for DRM to produce syngas (CO and H₂). The abundance, low cost, excellent properties and environmentally friendly nature of these support materials are an added advantage. Herein, this review entails the recent advances in development of zeolite and clay-based catalysts for DRM. In addition, the review captured a discussion on emerging trends in engineered mesostructured DRM catalysts. Tailoring of their framework configuration, pore architecture, crystals morphology and incorporation of active phases have led to the discovery of novel, robust and high-performance catalysts. Notably, advances recorded in the catalysts synthesis procedures and characterization methods were also highlighted and elaborately discussed. It is expected that this review provide a comprehensive roadmap in the quest for an economically and industrially potent catalyst for syngas production via DRM.     

Carbon dioxide reforming of methane over nickel catalysts supported on TiO2(001) nanosheets

As we all know, the critical problem of nickel catalysts for carbon dioxide reforming of methane is the deactivation of catalysts due to the carbon deposition and sintering of the active components under high temperature. It was reported that anatase TiO₂ nanosheets with high-energy (001) facets had strong interaction with nickel, which was probably beneficial to resist sintering of nickel nanoparticles and to eliminate deposited carbon via oxygen migration. In this study, Ni nanoparticles were supported on TiO2 nanosheets with exposed high-energy (001) facets. The Ni/TiO₂(001) catalysts were characterized by means of X-ray diffraction, transmission electron microscopy, physisorption of N₂, X-ray photoelectron spectroscopy and H₂ temperature-programmed reduction, and the spent catalysts were characterized by Roman and thermogravimetry analysis. The catalytic performance of Ni/TiO₂(001) catalysts were measured for carbon dioxide reforming of methane reaction. It was found that the prepared Ni/TiO₂(001) catalysts showed reasonably higher catalytic activity and stability compared with the nickel catalyst supported on commercial titanium oxide (P25). The high dispersion of nickel nanoparticles of Ni/TiO₂(001) catalysts was helpful to the resistance towards carbon deposition and the strong metal-support interaction was helpful to the resistance towards nickel sintering on account of the unusual surface properties of TiO₂(001).     

Enhanced activity of Co catalysts supported on tungsten carbide-activated carbon for CO2 reforming of CH4 to produce syngas

Carbon materials are widely used as catalysts or supports due to their excellent properties. In this paper, the tungsten carbide-activated carbon (WC-AC) composite support was successfully prepared by in-situ carburizing on AC matrix, which is characterized by the covalent anchoring of WC on the AC support. The active metal Co was supported on WC-AC for dry reforming of methane (DRM). Samples were analyzed by N₂ physisorption measurements, XRD, XPS, H₂-TPR, H₂-TPD, CH₄&CO₂-TPSR, TG-DTG. The WC-AC stabilizes the disturbance of C in AC, alleviates the gasification effect of CO₂ and increases the active sites for CH₄ cracking. Moreover, WC provides a resistance-less bridge suitable for the Co³⁺ → Co²⁺, resulting in a high Co²⁺/Co³⁺ ratio on the catalyst surface. This enhances the interaction between the Co species and the WC-AC, thereby enhancing the CH₄ activation. In the process of WC-AC promoting Co³⁺→Co²⁺, the catalyst surface is accompanied by the generation of oxygen vacancies. This can enhance the dissociative adsorption of CO₂ on surface of the WC-cobalt oxide, and at the same time increase the relative proportion of adsorbed oxygen on the catalyst surface, thereby effectively inhibiting the formation of coke. However, the small amount of graphitic carbon generated due to the strong coupling of WC and Co is the main reason for deactivation of Co/WC-AC.     

Optimization of renewable hydrogen-rich syngas production from catalytic reforming of greenhouse gases (CH4 and CO2) over calcium iron oxide supported nickel catalyst

Multi-response optimization of hydrogen-rich syngas from catalytic reforming of greenhouses (methane and carbon dioxide over Calcium iron oxide supported Nickel (15 wt%Ni/CaFe₂O₄) catalyst was performed by varying reaction temperature (700–800 °C), feed ratio (0.4–1.0) and gas hourly space velocity (10,000–60,000 h^?1)) using response surface methodology. Four response surface methodology (RSM) models were obtained for the prediction of reactant conversion and the product yield. The analysis of variance (ANOVA) conducted on the model showed that the parameters have significant effect on the responses. Optimum conditions for the methane dry reforming over the 15 wt%Ni/CaFe₂O₄ catalyst were obtained at reaction temperature, feed ratio and gas hourly space velocity (GHSV) of 832.45 °C, 0.96 and 35,000 mL g^?1 h^?1 respectively with overall desirability value of 0.999 resulting in the highest methane (CH₄) and carbon dioxide (CO₂) conversions of 85.00%, 88.00% and hydrogen (H₂) and carbon monoxide (CO) yields of 77.82% and 75.76%, respectively.     

Production of syngas via CO2 methane reforming process: Effect of cerium and calcium promoters on the performance of Ni-MSC catalysts

The dry reforming of methane (DRM) over Ni-MSC catalysts promoted by different Ce/Ca ratios was compared. The different Ce/Ca ratios proportions were introduced by coprecipitation. The catalysts with different content of promoter were characterized by N₂ adsorption, XRD, H₂-TPR and TEM. XRD and TEM results demonstrated that Ni–4Ce1Ca-MSC catalyst modified with high Ce/Ca had the best dispersibility and the smallest Ni particle size, resulting in more surface active sites. The synergy between Ce and Ca made a great contribution to prohibiting the generation of carbon deposits and the sintering of active metal during DRM procession. In contrast, catalysts modified only with Ca or Ce exhibited poor catalytic performance, resulting in significant deposition of carbon on the surface of the Ni–5Ca-MSC catalyst. In addition, the high Ce concentration greatly increases the oxygen storage capacity, which helps to form oxygen vacancies by mutual conversion of Ce⁴⁺/Ce³⁺ and Ni²⁺/Ni⁰.     

Catalytic performance and characterization of Neodymium-containing mesoporous silica supported nickel catalysts for methane reforming to syngas

Ordered mesoporous silica materials based on nickel and other elements have been extensively studied because controlling the size of metal nanoparticles is an effective method to tune the superficial physicochemical process. Neodymium (Nd)-promoted mesoporous silica xNdMS (x: molar ratio of Nd/Si = 0.01, 0.02, 0.04, 0.06) were prepared through a sol–gel strategy. Nickel-based catalysts with high dispersion by using xNdMS as supports were investigated for methane reforming with carbon dioxide and/or oxygen to produce syngas. xNdMS supports and nickel catalysts were examined by combining textural, structural, local and surface information. The characterization results showed that Nd was successfully incorporated into the mesoporous framework of MS and Nd was beneficial to improve the metal dispersion. All Nd-promoted Ni/MS catalysts were effective for the methane reforming reaction. Ni/0.04NdMS catalyst exhibited the highest initial catalytic activity during 12 h time on stream, which was attributed to its high metal dispersion, more basic sites and the strengthened nickel-support interaction. The readily deactivation and poorest catalytic activity of Ni/MS catalyst were due to the serious oxidation of metallic nickel under reaction medium.     

Metal oxide (MgO,CaO, and La2O3) promoted Ni-Ce0.8Zr0.2O2 catalysts for H2 and CO production from two major greenhouse gases

The metal oxide (MgO, CaO, and La₂O₃) promoted Ni-Ce_0.8Zr_0.2O₂ catalysts have been applied for carbon dioxide reforming of methane (CDR) reaction and investigated the coke formation and sintering phenomenon in used catalysts. The Ni-MgO-Ce_0.8Zr_0.2O₂ catalyst exhibits high activity and stability at a very high gas hourly space velocity of 480,000 h⁻¹, resulting from high resistance to coke formation and Ni sintering. This is mainly due to small Ni crystallite size, strong basicity of MgO, and an intimate interaction between Ni and MgO.     

Hydrogen and syngas production by methane dry reforming on SBA-15 supported nickel catalysts: On the effect of promotion by Ce0.75Zr0.25O2 mixed oxide

In this work, the effects of doping Ni-based SBA-15 catalysts with Ceria–Zirconia mixed oxide (CZ) on the activity and stability of these catalysts during syngas production by methane dry reforming (MDR) were investigated and compared with the activity and stability of unmodified Ni/SBA-15. The above catalysts were prepared by incipient wetness impregnation (IWI) with different impregnation strategy. The samples were characterized by nitrogen physisorption, X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), temperature programmed reduction (TPR) and H₂ chemisorption. The results indicated that the unmodified Ni/SBA-15 showed clear deactivation especially in the first period of the stability test and between 600 °C and 630 °C during the activity test whereas the CZ modified samples had better stability.     

Enhancement of plasma-assisted catalytic CO2 reforming of CH4 to syngas by avoiding outside air discharges from ground electrode

This work presents the effects of the insulation of ground electrode and operating parameters on CO₂ reforming of CH₄ to syngas in a coaxial-cylindrical dielectric barrier discharge (DBD) plasma reactor coupled with Ni/α-Al₂O₃ catalyst. For the conventional plasma reactor, abnormal outside discharge inevitably ignites and develops from the ground electrode, giving rise to the formation of harmful substances (e.g., NO_x) and the waste of energy. The power dissipation for the conventional reactor therefore includes both that used for the dry reforming reactions and the loss of energy due to the air discharge. The new finding of this work is that by covering the ground electrode with an insulating oil jacket, not only the NO_x formation is prevented but also the conversion rates, product selectivity and energy efficiency are largely enhanced by roughly 30, 10 and 100% at a specific energy input of about 47 kJ, respectively. The results are associated with the extinguishment of the discharge occurring outside the reactor, which is usually neglected when designing DBD reactors.     

Physico-chemical properties and syngas production via dry reforming of methane over NiAl2O4 catalyst

Nano-particles of NiAl₂O₄ were prepared by co-precipitation and their bulk and surface were characterized by XRD, Raman spectroscopy, N₂-adsorption-desorption analysis, SEM-EDS and XPS. The reducibility was studied by TPR and HTXRD techniques under H₂ atmosphere. The synthetized catalyst was made of NiAl₂O₄ spinel oxide as main phase and of NiO (10%) free oxide. Interestingly, it was shown that the surface was richer in Al species. The catalytic performances in methane dry reforming were evaluated without H₂-pretreatment of catalyst. A very high activity was observed with conversion of methane and CO₂ at 750 °C of 84 and 90 mol%, respectively and high H₂/CO ratio. The amount of coke deposited during the reaction on this spinel was ～3.6%. The physico-chemical properties of the catalyst on their behavior in the dry reforming of methane are discussed.     

Lanthanide oxide modified nickel supported on mesoporous silica catalysts for dry reforming of methane

Addition of rare earth oxide, especially lanthanide oxide, was regarded as a promising strategy to improve the carbon resistance for Nickel-based catalysts in dry reforming of methane (DRM). In this work, Nickel-based catalysts containing lanthanide oxides (NiLa/SiO₂, NiCe/SiO₂, NiSm/SiO₂, and NiGd/SiO₂) were prepared and employed to catalyze DRM. Lanthanide oxide affected the formation of Ni nanoparticles in different size. In NiLa/SiO₂ and NiCe/SiO₂, Ni nanoparticles maintained relatively small size (4 nm), while in NiSm/SiO₂ and NiGd/SiO₂, nickel particles were in large size (8 nm). NiLa/SiO₂ and NiCe/SiO₂ exhibited better stability than the other two catalysts, with CH₄ conversion decreasing from 64.6 to 57.6% and 61.6 to 60.3%, respectively in 10 h on stream. The kinetic study confirmed that adding lanthanide oxide significantly affected the activation energy of CH₄ dissociation and CO₂ dissociation. Compared to monometallic Ni/SiO₂, the presence of Sm and Gd suppressed CO₂ dissociation, and introduction of Ce and La effectively promoted CO₂ dissociation. These characters contributed to the higher carbon resistance and good stability for NiLa/SiO₂ and NiCe/SiO₂ catalysts in DRM reaction.     

Effect of O2 and temperature on the catalytic performance of Ni/Al2O3 and Ni/MgAl2O4 for the dry reforming of methane (DRM)

Al₂O₃ and MgAl₂O₄ supported 10% (w/w) Ni catalysts having a dispersion of 1.5 and 2.0% are active for DRM at 600 and 750 °C. High temperature reduction of both the calcined catalysts resulted in metallic Ni being formed, suggesting strong support metal interactions. The CH₄ and CO₂ conversion during DRM are relatively constant with time-on-stream, and are higher for Ni/MgAl₂O₄ than Ni/Al₂O₃. Carbon-whiskers are also detected on both catalysts. O₂ co-feed of 2.6% (v/v) and increasing reaction temperature to 750 °C helped in decreasing the amount of carbon deposited, except for Ni/MgAl₂O₄ at 600 °C. Furthermore, higher conversions and H₂/CO ratios are achieved. It appears that on spent Ni/MgAl₂O₄ a different type of carbon species was formed, and this carbon species was difficult to remove by oxygen at 600 °C. Thus, co-feeding O₂, using an appropriate temperature, and choosing a suitable support can reduce the carbon present on the nickel catalysts during DRM.     

Syngas production via dry reforming of methane over CeO2 modified Ni/Al2O3 catalysts

Syngas production via dry reforming of methane (DRM) was experimentally investigated using Ni-based catalyst. Ni/Al₂O₃ modification with CeO₂ addition and O₂ addition in the reactant were employed in this study to suppress carbon deposition and to enhance catalyst activity. It was found that DRM performance can be enhanced using CeO₂ modified Ni/Al₂O₃ catalyst due to CeAlO₃ formation. However, an optimum amount of CeO₂ loading exists to obtain the best DRM performance due to the decrease in specific surface area as the CeO₂ loading increases. Without O₂ addition, the reverse water-gas shift reaction plays an important role in DRM. It was found that CH₄ conversion and CO yield were enhanced while CO₂ conversion and H₂ yield are decreased as the CO₂ amount in feedstock increased in DRM. With O₂ addition in the fed reactant, it was found that the methane oxidation reaction plays an important role in DRM. CH₄ conversion can be enhanced by O₂ addition. However, decreases in CO₂ conversion and H₂ and CO yields occurred due to greater H₂O and CO₂ productions from the methane oxidation reaction. The thermogravimetric analysis (TGA) results showed that CeO₂ modified Ni/Al₂O₃ catalyst would have the lowest amount of carbon deposition when O₂ is introduced into the reaction.     

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.     

Methane dry (CO2) reforming to syngas (H2/CO) in catalytic process: From experimental study and DFT calculations

Dry reforming of methane (DRM) is a promising reaction, it could convert two greenhouse gases CO₂ and CH₄ into syngas (CO and H₂) which could provide a mixed fuel for daily life or chemical feedstock for industrial application. Transition metals were widely applied in this process, however, single component of transition metal catalysts could not meet the stability, selectivity and activity demands simultaneously. And the coke formation on the catalysts is the major barrier to the commercialization of DRM. This review presents a systematic discussion and analysis of methane dry reforming to syngas in the catalytic process from both experimental study and density functional theory (DFT) calculation based on recent research. It includes catalytic performance test of activity, selectivity and stability in DRM on monometallic and bimetallic systems, and also gives the discussion of carbon formation in the former parts. The later parts focus on CH₄ and CO₂ activation over monometal and bimetal surface using DFT simulation. The rate determining step and reaction mechanisms involved in DRM are obtained based on thermodynamic analysis and microkinetic model. In the end, we give our outlook to the design and preparation of good performance catalysts as well as further theoretical simulation and analysis in DRM. This review could provide some useful information for going into methane dry reforming from both experimental application and atomic scale.