NiO MgO Solid Solution Research Articles

Enhancement of CO2 adsorption and oxygen transfer properties on γ-Al2O3 support through surface modification with MgO-ZrO2 for coke suppression over Ni catalyst in CO2 reforming of methane

This work focuses on employing commercial γ-Al2O3 for surface modification with MgO-ZrO2 mixed oxide to enhance the potential of CO2 adsorption and oxygen mobility. This enhancement facilitates its application as a support in catalysts for CO2 utilization such as CO2 reforming of methane (CRM). To achieve this perspective, γ-Al2O3 was modified with 10 wt.% of various MgO and ZrO2 contents (MgO:ZrO2= 10:0, 9:1,7:3, 5:5, 3:7, 1:9 and 0:10) using the impregnation method. All samples including unmodified γ-Al2O3 (Al) were characterized. Due to the increase in basicity and oxygen transfer around the surface, the improvement of the CO2 adsorption was observed on γ-Al2O3 modified with 9 wt.% MgO-1 wt.% ZrO2 (9Mg1ZrAl) and 10 wt.% MgO (10MgAl), respectively. An application of these two superior samples as a support of 10 wt.% Ni (10Ni) catalysts for CRM was investigated and compared with an unmodified γ-Al2O3. Characterization results suggest the formation of NiO-MgO solid solution at the surface due to the decrease in metal-support interaction and the increase in metal dispersion. The Ni catalysts with the surface-modified support show higher CO2 activity that raises carbon deposition resistance. The greatest coke prevention was observed on 10Ni/9Mg1ZrAl that lowers the coke deposition by 42% compared to 10Ni/Al. It indicates that the composition of this modification allowed very low ZrO2 portion to merge with MgO and MgO to form solid solution with NiO. This enables the 10Ni/9Mg1ZrAl catalyst to generate labile oxygens which can be conveyed to the Ni metal sites on the catalyst.

Highly porous Ni/MgO-ZrO2 catalysts for dry reforming of methane and the effects of MgO addition on the mechanisms

Dry reforming of methane (DRM) is a promising pathway to convert greenhouse gas into syngas. However, the commonly used Ni based catalysts suffer deactivation due to severe sintering and coking. In this paper, a series of porous Ni/MgO-ZrO2 catalysts (5Ni/xM(1-x)Z, x = 0, 20, 40, 60, 80 wt%, respectively) with high specific surface area were synthesized by a facile combustion method followed by incipient impregnation. It is found that the appropriate amount of MgO (40 %) addition in ZrO2 favors high porosity and high specific area. More MgO enhances the basicity of the catalyst as well as the metal-support interaction (MSI) by the formation of NiO-MgO solid solution, thus improving DRM activity and coking resistance. However, excessive MgO addition leads to over-strong MSI and lower porosity, resulting in lower DRM activity. The catalyst with 40 % MgO addition (5Ni/40M60Z) exhibits the best activity (conversions of CH4 ∼ 76 %, CO2 ∼ 83 %) and stability (>50 h) at high GHSV = 96000 ml/gcat·h and 750 °C. in situ DRIFTS reveals the mechanism that MgO addition improves DRM activity and stability. Compared with ZrO2 where CO2 adsorbs as monodentate carbonate, CO2 tends to adsorb on 40 %MgO-60 %ZrO2 as bidentate carbonate and then easily transfer to more stable intermediate bidentate formate, thus improving DRM activity and coking resistance. This study provides new insights on the role of Mg addition in Ni/MgO-ZrO2 DRM catalysts.

Rapid fabrication of Ni supported MgO-ZrO2 catalysts via solution combustion synthesis for steam reforming of methane for hydrogen production

In this study, we introduced a solution combustion as a simple, efficient, and rapid technique for synthesis of a nanostructured Ni catalyst supported on MgO-ZrO2 for hydrogen production by steam reforming of methane. A series of Ni/MgO-ZrO2 catalysts with different Ni contents were prepared and investigated to observe a suitable Ni loading content. The evaluation of catalytic performance of the as-prepared catalysts was performed in a packed-bed reactor at 700 °C and atmospheric pressure at steam to carbon ratio (S/C) of 2. As a result, the 20Ni/20MgO-ZrO2 catalyst exhibited not only outstanding catalytic performances, but also minimized coke deposits, attributed to the presence of oxygen vacancies of MgO-ZrO2 solid solution. In addition, combustion synthesis could result in formation of NiO-MgO solid solution, boosting uniform dispersion of Ni particles. A durability test of the optimized 20Ni/20MgO-ZrO2 catalyst was conducted at 700 °C for 50 h, revealing a near constant methane conversion of approximately 92.9%. Although filamentous carbon and carbon encapsulation were observed on the surface of spent catalyst, there is no significant negative impact on the steam reforming performance. In conclusion, this present work highlights the efficacy of the solution combustion method for synthesis of nanostructured Ni/MgO-ZrO2 catalysts with superior catalytic performance and less coke deposits for hydrogen production from methane steam reforming.

Nano-crystalline NiO-MgO/NiAl2O4 catalyst for coking free low temperature partial oxidation of methane

Here, we report an ultra-small-sized nano-crystalline NiO-MgO/NiAl2O4 catalyst for coking-free partial oxidation of methane reaction at low temperature (450 °C). The catalyst was tested in a packed-bed reactor over a temperature range of 350 to 850 °C. The NiO-MgO/NiAl2O4 catalyst was optimized for calcination temperature and nickel content. The best-optimized sample was then tested for different gas hourly space velocities (GHSVs), resulting in 99 % CH4 conversion and varying H2/CO selectivities from 90 % to 70 % at 450 °C. A stability test was conducted at 500 °C for 100 h for stream on reaction conditions, resulting in 95 % CH4 conversion, 90 % H2 selectivity, and 60 % CO selectivity without any significant deactivation. The excellent catalytic activity and stable performance were attributed to the ultra-small size and nanocrystalline structure of NiO-MgO, as well as the presence of lattice oxygen reservoirs. Additionally, the synergistic interaction between the NiO-MgO solid solution and the support NiAl2O4 contributed to these properties.

Upcycling of hazardous plastic waste by CO2 transformation-enhanced steam reforming over MgO-promoted Ni/C bifunctional catalyst

Disposing hazardous plastic waste (e.g., used masks) poses a challenging issue, as these waste plastics often carry the risk of virus infection. CO2 transformation-enhanced steam reforming (CTESR) route was developed and newly synthesized dual-support Ni bifunctional catalysts were explored for the upcycling of disposed mask. Among the single-support Ni catalysts, Ni/CaO presented a high H2 yield (52.18 mmol/g), but it was inferior to Ni/MgO and Ni/C in terms of CO2 transformation capacity. Importantly, Ni/MgO demonstrated the lowest carbon deposition (∼2.67 wt%) due to the interaction between MgO and NiO, forming a NiO-MgO solid solution. In this sense, dual-support Ni catalysts were prepared to achieve extensive H2 production and CO2 reduction. Dual-support Ni/MgO-C was superior to other dual-support catalysts in terms of H2 selectivity (57.77 vol%), H2 yield (51.58 mmol/g), CO2 emission (1.72 mmol/g), and H2 production efficiency (ƞ: 0.74 g CO2/g H2). Moreover, it presented a remarkable synergistic effect on H2 yield and production efficiency, with an enhancement of 117.27 % and 32.58 %, respectively. The super catalytic performance was attributed to the unique properties of Ni/MgO-C, high dispersion of Ni/NiO active core, and proper interaction of Ni/NiO with the dual supports. In addition, MgO-promoted Ni/C catalysts with multiple MgO proportions were examined. Ni/MgO5-C5 was identified as the optimal bifunctional catalyst for H2-rich syngas production and CO2 elimination. Overall, this study established a highly effective and promising route by using dual-support Ni catalysts for upcycling hazardous plastic waste into H2-rich syngas while suppressing CO2 emission.

Green hydrogen Production from the oxidative reform of clean biogas over Ni/MgO-Nb2O5 catalysts

Synthesis gas has a variety of applications ranging from its transformation into Fischer-Tropsch fuels, its processing to produce pure hydrogen, and even its direct combustion to generate energy, among many other applications. The objective of this work was the conversion of a model of biogas (clean biogas) into synthesis gas, H2 /CO, through oxidative reforming of methane over NiO/MgO/Nb2O5 catalysts. The catalysts in this work were prepared by impregnation and calcination (at 750ºC) and subsequently characterized by Energy Dispersive X-ray spectroscopy (EDX), Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), Nitrogen Adsorption-Desorption (BET method) and Temperature Programmed Reduction with H2 (TPR). Finally, these catalysts were tested in the oxidative reform of methane (molar ratio of 1.5CH4:1CO2:0.25O2) at 750 ºC, 100mg of catalyst at a total flow of 110 mL.min-1, and 1 atm (inside the reactor). According to the results, it was verified that the catalyst composed of the NiO/MgO mixture is composed of the NiO-MgO solid solution, whereas the NiO/MgO/Nb2O5 catalysts are also formed by nickel niobate (NiNb2O6). All catalysts showed catalytic activity in the oxidative form of biogas, NiMg, Ni60NbMg, and Ni40NbMg catalysts showed the highest conversion value. The efficiency of the catalysts in the oxidative reforming of biogas improved gradually as the %MgO increased in the NiO/MgO/Nb2O5 system. The characterization of the catalyst after the reaction demonstrated that the carbon formed is of the filamentous type.

Alkaline earth metal modified nickel nanoparticles supported on exfoliated g-C3N4 for atmospheric CO2 methanation

Alkaline earth metals such as magnesium (Mg) and calcium (Ca) are promising catalyst promoters for CO2 methanation owing to their exceptional basic characteristics. This study details the development of nickel-based catalysts promoted with Mg and Ca supported by exfoliated graphitic carbon nitride (eg-C3N4). The catalysts were synthesised using a facile impregnation technique and characterised using N2 physisorption, XRD, TEM, XPS, H2-TPR and CO2-TPD. The Mg-promoted catalyst showed a greater number of mesopores, better dispersion of small Ni NPs, stronger metal-support interaction and enhanced moderate basic sites compared to Ni/eg-C3N4. Conversely, the presence of bulk CaCO3 species in the Ca-doped catalyst negatively affected the textural properties and basicity. Ni-Mg/eg-C3N4 catalyst demonstrated superior methanation activity with CO2 conversion (XCO2) of 77% and CH4 selectivity (SCH4) greater than 99% at 322 °C. This is mainly attributed to the creation of a NiO-MgO solid solution which enhances the interaction between metal and support, leading to the promotion of small and highly dispersed Ni NPs. Moreover, the incorporation of an Mg promoter generates Lewis basic sites and alters the basicity of the eg-C3N4 support, increasing the number of effective CO2 adsorption sites. The synergy between the Mg dopant and eg-C3N4 support significantly contributes to the high activity and stability for low-temperature CO2 methanation.

Combined Steam and CO2 Reforming of Methane over Ni-Based CeO2-MgO Catalysts: Impacts of Preparation Mode and Pd Addition

The sol–gel template technique makes it possible to synthesize a stable and efficient nickel catalyst based on magnesium-modified cerium oxide Ce0.5Mg0.5O1.5 for the combined steam and CO2 reforming of methane. To stabilize dispersed forms of the active component in the matrix of the support, the catalysts were synthesized by changing the support precursor (cerium acetate and chloride), the active component composition (Ni, NiPd) and the method of introducing nanoparticles. The relationship was established between the physicochemical and catalytic characteristics of the samples. The use of cerium acetate as a support precursor provided smaller pore and crystallite sizes of the support, a stabilization of the dispersed forms of the active component, and excellent catalytic characteristics. The introduction of Pd into the Ni nanoparticles (Pd/Ni = 0.03) increased the resistance of the active component to sintering during the reaction, ensuring stable operation for 25 h of operation. The increased stability was due to a higher concentration of defective oxygen, a higher dispersion of bimetallic NiPd nanoparticles, and the Ni clusters strongly interacting with the NiO-MgO solid solution. An efficient and stable Ni0.194Pd0.006Ce0.4Mg0.4O1.4 catalyst for the conversion of CO2 into important chemicals was developed. With the optimal composition and synthesis conditions of the catalyst, the yield of the target products was more than 75%.

NiO-MgO Prepared by the Complex-Decomposition Method as a Catalyst for Carbon Dioxide Reforming of Methane

The NiO-MgO solid solution has been proven to be an efficient catalyst for the carbon dioxide reforming of methane (CRM). However, the challenge is still there for the facilely controlled synthesis of the single-phase solid solution with the uniform composition, and the interactions between NiO and MgO are not consistently correlated with the CRM performance. To address these issues, in this work, the complex-decomposition method was applied to regulate the chemical and structural properties of NiO-MgO catalysts via simply changing the complexing agent, calcination temperature, and Ni/Mg molar ratio. The catalysts were comparatively evaluated for CRM under severe reaction conditions of 750 °C, 0.1 MPa, CH4/CO2 = 1, and a gas hourly space velocity of 60000 mL·g−1·h−1. Irrespective of the complexing agents investigated, NiO-MgO solid solution was exclusively formed. However, the structural and reductive properties of the NiO-MgO catalysts were strongly dependent on the complexing agent, which is reasonably explained as the varied coordinative capabilities of the complexing agent with the metal cations. Moreover, the highest CRM performance, i.e., the initial CH4 conversion of ~86% kept constant for a time-on-stream of 20 h, was achieved over the Ni0.1Mg0.9O catalyst by using glycine as the complexing agent and calcined at 800 °C. The characterization and CRM results vigorously confirmed that a good balance between the sintering and the in situ release of active metallic Ni under CRM reaction conditions was constructed over the NiO-MgO catalyst prepared using glycine as the complexing agent, leading to its highest stability. Considering the simple procedure of the complex-decomposition method and the convenient adjustment of the NiO and MgO interactions by simply changing the complexing agent and calcination temperature, the thus developed catalyst can be applied for extensive understanding the CRM mechanism, and extended for large-scale preparation.

Customized Ni-MgO-ZrO2 catalysts for the dry reforming of methane using coke oven gas: Optimizing the MgO content

Ni-ZrO2 and Ni-MgO-ZrO2 catalysts were prepared by the stepwise control of the MgO content in the Ni-ZrO2 catalyst to develop a customized catalyst for the dry reforming (DRM) reaction utilizing coke oven gas (COG). The difference in MgO content affected the physicochemical properties of the catalysts. As MgO was added and the amount increased, formation of the NiO-MgO solid solution was promoted, so the Ni0 dispersion increased, but the reduction degree decreased due to strong metal-support interactions. On the other hand, basicity of the catalyst was not simply enhanced as the MgO content increased but was also affected by the degree of incorporation of Mg2+ ions into the tetragonal-ZrO2 lattice. We systematically changed the MgO content to select a catalyst that could show excellent performance in the actual process, while applying the catalyst to various reaction tests. Reaction conditions for screening of catalytic performances were derived by calculating thermodynamic equilibrium to minimize carbon deposition and maximize CO yield. As a result of catalytic evaluation, the Ni-30MgO-ZrO2 catalyst exhibited the highest catalytic activity and stability in the COG-DRM reaction. In addition, the Ni-30MgO-ZrO2 catalyst showed high stability through a long-term stability test and a temperature swing test (800–900 °C), indicating the possibility of commercialization for the target reaction.

Two birds with one stone: MgO promoted Ni-CaO as stable and coke-resistant bifunctional materials for integrated CO2 capture and conversion

Calcium Looping coupling with CH4 dry reforming (CaLDRM) is a promising technology to achieve CO2 capture and in-situ conversion to syngas, thereby attracting much attention recently. However, the significant coke deposition and reduced activity of the Ni-CaO based bifunctional materials hinder its practical application. In this work, low-cost MgO was utilized to promote Ni-CaO bifunctional material, which successfully drives cyclic CO2 capture and conversion. On the one hand, MgO act as a stabilizer to inhibit CaO sintering, acquiring excellent CO2 capture ability and cycle stability. After 20 cycles, the 10 wt% MgO promoted Ni-CaO bifunctional materials (Ni-Ca10Mg) maintained the CO2 capture capacity of 0.53 gCO2/gmaterial, much higher than the unmodified material. On the other hand, MgO can form NiO-MgO solid solution with NiO, bringing fine Ni particle sizes and abundant oxygen species. Thanks to the effect of NiO-MgO solid solution, Ni-Ca10Mg demonstrated stable CO2 conversion and syngas yield during the isothermal CaLDRM cycles, while the coke depositions are only 0.0395 gcoke/gmaterial after 10 CaLDRM cycles, corresponding to 37.2 % of unmodified material.

The bulk and supported perovskite-type catalysts for the CO2 reforming of methane: The effect of ceria and magnesia

BackgroundThe bulk or supported nickel catalysts are active in the dry reforming of methane to produce syngas. The nickel-based catalysts are deactivated quickly due to the metal sintering and coke deposition. Perovskite catalysts are stable, enhance the dispersion of the active sites, and resist metal sintering and coke deposition. The coke deposition is inhibited by increasing the CO2 adsorption and oxidation of the deposited coke. MethodsA series of ceria-doped perovskite catalysts La1-xCexNiO3, LaNi1-xCexO3 and magnesia-modified-alumina supported perovskite-type catalysts were prepared via the sol-gel method. The prepared catalysts were thoroughly characterized via state-of-the-art characterization techniques. Significant findingsThe incorporation of ceria assisted the supported catalysts in forming a dispersed phase at low loading and forming other NiO or NiO-MgO (solid solution) NiAl2O4 and MgAl2O4 (spinel phase). The catalytic activity for the CO2 reforming of methane reaction increased with the addition of magnesia and the substitution of La-ion with tetravalent metal cation (ceria). The doping of ceria increased the stability of the catalyst. The bulk catalyst La0.5Ce0.5NiO3 exhibited promising catalytic activity. The magnesia-modified-alumina-supported catalyst (50La0.5Ce0.5NiO3/8MgO-Al2O3) was more active than the alumina-supported or bulk-perovskite catalysts with low coke deposition and higher percent conversion of CH4 (97%) and CO2 (99%) at 1073 K.

Propane dry reforming over highly active NiO-MgO solid solution catalyst for synthesis gas production

In the present study, the textural characteristics and catalytic efficiency of the NiO(x)-MgO solid-solution catalysts (x = 10,15,20, and 25 wt.%) were determined in CO2 reforming of propane. All samples were fabricated by the simple mechanochemical preparation route. The chemicophysical characteristics of the synthesized catalysts were determined using XRD, BET, H2-TPR, TPO, and SEM exams. The obtained results demonstrated that the physicochemical properties and catalytic activity of the samples were affected with the increment in NiO content, which is assigned to the change in the concentration of active sites and improvement of the reduction features. The NiO(25)-MgO catalyst was selected as the sample with the highest activity, and the effect of the operating factors and calcination temperature were studied over this catalyst. Also, the TPO analysis showed that the whisker carbon was formed on the spent catalyst and the sample with 25 wt.% Ni possessed the highest amount of deposited carbon. Moreover, the initial catalytic activity of all catalysts was not changed during 300 min time on stream.

Influence of Supports on the Catalytic Activity and Coke Resistance of Ni Catalyst in Dry Reforming of Methane

The dependence of the catalytic activity and coke resistance of Ni-based catalysts on the support type was investigated in the dry reforming of methane (DRM). Catalysts were prepared using incipient wetness impregnation and analyzed using ICP-OES, BET-BJH, XRD, H2-chemisorption, H2-TPR, and CO2-TPD. DRM was performed at 600–750 °C at 144,000 mL/gcat∙h of GHSV (CH4/CO2/N2 = 1/1/1). Ni/Al2O3 and Ni/MgO catalysts formed NiAl2O4 and NiO-MgO solid solutions, respectively, owing to strong binding between the metal and support. In contrast, MgO-Al2O3 and MgAl2O4 supports suppressed NiAl2O4 and NiO-MgO solid solution formation, due to Mg addition, with high metal dispersions of 4.6 and 6.6%, respectively. In the DRM reaction, the Ni/MgO-Al2O3 and Ni/MgAl2O4 catalysts showed high CH4 conversions of 78.1 and 76.8%, respectively, compared with Ni/Al2O3 and Ni/MgO at 750 °C. A stability test was performed at 600 °C for 20 h. A coke study of the spent catalysts was performed using SEM and TGA. Alkaline-earth metal-containing catalysts Ni/MgO-Al2O3 and Ni/MgAl2O4 with strong CO2 adsorption properties showed 20 wt% reduction in carbon deposition compared to commercial catalysts. Therefore, the support and basic properties of the catalyst significantly influenced the catalyst performance and coke resistance in the DRM.

Catalytic pyrolysis of toluene as biomass tar model component using Ni/HZSM-5 modified by CeO2 and MgO promoters

Thermochemical conversion technology is a promising chemical method for removal of biomass tar. In this study, Ni/HZSM-5 catalyst modified by CeO2 and MgO promoters were prepared by ultrasonic-assisted excessive impregnation method. Toluene was selected as the representative model component of biomass tar, and the pyrolysis experiments were carried out in a tubular fixed bed reactor. Fresh and reacted catalysts have been characterized. The results revealed a similar initial activity for different loadings of same promoter. The stability of Ni-Ce catalysts increased gradually with increasing of Ce loading. In particular, Ni-4%Ce/HZSM-5 catalyst has the best catalytic activity with the toluene conversion of 94.5%, the yield of total gas of 107 mL/g, the gaseous efficiency of 68 wt.%. The BET surface areas as large as 206.9 m2/g with an average pore size of 3.2 nm assisted NiO particles dispersed on the surface of HZSM-5 support. Although the performance of Ni-4%Ce/HZSM-5 catalyst was better, the surface of its also formed char with an elongated fiber. However, the low-catalytic performance of Ni-Mg/HZSM-5 was due to the instability of active center NiO-MgO solid solution. This study revealed the influences of promoter types, promoter loadings, and the potential mechanism of similar catalytic performance on the preparation process of Ni-based catalysts.

High-Efficiency, Coke Deposition-Resistant Ni-Cao Based Catalyst for Integrated Co2 Capture and Conversion: Effect of Nio-Mgo Solid Solution

High-Efficiency, Coke Deposition-Resistant Ni-Cao Based Catalyst for Integrated Co2 Capture and Conversion: Effect of Nio-Mgo Solid Solution

Enhanced activity and stability of MgO-promoted Ni/Al2O3 catalyst for dry reforming of methane: Role of MgO

Highly dispersed nickel nanoparticles (NPs) were deposited on Al2O3 NPs by atomic layer deposition (ALD). Various amounts of MgO were loaded on Ni/Al2O3 catalysts by the incipient wetness (IW) method for dry reforming of methane. Fresh and used catalysts were systematically characterized to reveal the effects of MgO on the catalytic performance. MgO was found to increase the basic amount and basic strength of catalyst surfaces, which provided additional surface oxygen species and assisted the adsorption and activation of CO2. Although the formation of NiO-MgO solid solution, during the calcination of incipient wetness, did not improve the overall reducibility, the Ni NPs from NiO-MgO solid solution after reduction formed an intimate interaction with MgO, which could inhibit Ni NPs from sintering and provide sufficient metal-support interface for CO2 activation. The MgO-promoted Ni/Al2O3 reached a methane reforming rate of 1780 LCH4gNi−1 h−1 at 850 °C, which is 26% more than that of the pristine Ni/Al2O3. The higher CO2 activity enhanced the oxidation rate of the surface carbon generated from side-reactions, thereby resulting in a higher reforming rate and inhibiting coke formation, especially the detrimental graphitic encapsulating carbon on the active nickel surface.

Cellulose assisted combustion synthesis of high surface area Ni-MgO catalysts: Mechanistic studies

The objective of this study was to determine the combustion mechanism of cellulose paper impregnated with Mg(NO3)2, Ni(NO3)2, glycine solutions, and their different combinations. It was established that the combustion mechanism changes as a function of the impregnated media composition. In the Mg(NO3)2-cellulose system, Mg2+ ions strongly catalyze cellulose pyrolysis; hence no atmospheric oxygen is needed for the self-sustained combustion reaction. In the Ni(NO3)2-cellulose system, Ni2+ ions catalyze pyrolysis at a lower rate, and atmospheric oxygen assists the combustion wave propagation. In glycine containing systems, glycine blocks the ability of metal cations to catalyze the early cellulose pyrolysis, and the combustion front propagates due to the exothermic reactions between metal nitrates and glycine. The above mechanisms influence the microstructure of the combustion products. Due to the near-complete degradation of cellulose fibers during the Mg2+ catalyzed pyrolytic combustion, the resulting materials had a highly porous, sponge-like microstructure with a BET surface area of up to 152 m2/g. After the reduction in hydrogen, Ni segregates to the surface of NiO-MgO solid solution, and the resulting catalysts exhibited near-equilibrium methane conversion during the dry reforming of methane reaction at 600°C with low carbon formation and no deactivation for 24 h of time on stream.

Promotional effect of magnesium oxide for a stable nickel-based catalyst in dry reforming of methane

The generation of synthesis gas (hydrogen and carbon monoxide mixture) from two global warming gases of carbon dioxide and methane via dry reforming is environmentally crucial and for the chemical industry as well. Herein, magnesium-promoted NiO supported on mesoporous zirconia, 5Ni/xMg–ZrO2 (x = 0, 3, 5, 7 wt%) were prepared by wet impregnation method and then were tested for syngas production via dry reforming of methane. The reaction temperature at 800 °C was found more catalytically active than that at 700 °C due to the endothermic feature of reaction which promotes efficient CH4 catalytic decomposition over Ni and Ni–Zr interface as confirmed by CH4–TSPR experiment. NiO–MgO solid solution interacted with ZrO2 support was found crucial and the reason for high CH4 and CO2 conversions. The highest catalyst stability of the 5Ni/3Mg–ZrO2 catalyst was explained by the ability of CO2 to partially oxidize the carbon deposit over the surface of the catalyst. A mole ratio of hydrogen to carbon monoxide near unity (H2/CO ~ 1) was obtained over 5Ni/ZrO2 and 5Ni/5Mg–ZrO2, implying the important role of basic sites. Our approach opens doors for designing cheap and stable dry reforming catalysts from two potent greenhouse gases which could be of great interest for many industrial applications, including syngas production and other value-added chemicals.

Propane steam reforming on mesoporous NiO–MgO–SiO2 catalysts for syngas production: Effect of the MgO/SiO2 molar ratio

In this research, a series of NiO-xMgO-SiO2 catalysts with various MgO/SiO2 molar ratios were prepared via precipitation method followed by a hydrothermal treatment in the presence of PVP as surfactant. The synergic effect between MgO and SiO2 leading to the various characteristic and catalytic performance during propane steam reforming was investigated in detail. The results showed that 15 wt% NiO-0.5MgO–SiO2 catalyst possessed the highest catalytic activity (68.9% conversion for C3H8 at 550 °C) with a negligible amount of carbon formation after 20 h of reaction duration. This superior catalytic performance can be attributed to the enhanced basicity strength along with strong metal-support interaction due to the formation of NiO–MgO solid solution, as confirmed by CO2-TPD and TPR analyses, respectively. In addition, the maximum hydrogen yield was obtained through the NiO–MgO sample because of higher progress in other hydrogen production routes as opposed to that of the propane steam reforming. It also can be suggested that relatively weak interaction between active sites and support was probably the main reason for unstable catalytic behavior of NiO–SiO2 sample with the lowest activity. This study confirms that the appropriate MgO/SiO2 ratio led to the sufficient metal-support interaction and delicate balance between acidic/basic sites, which was followed by the great activity, and coke resistance during PSR.