CO2-reforming of methane to produce syngas over Co-Ni/SBA-15 catalyst: Effect of support modifiers (Mg, La and Sc) on catalytic stability

Development of Ni-Mo carbide catalyst for production of syngas and CNTs by dry reforming of biogas

Biogas has been widely regarded as a promising source of renewable energy. Recently, the direct conversion of biogas over heterogeneous catalysts for the simultaneous production of syngas and carbon nanotubes exhibits a high potential for full utilization of biogas with great benefits. Involving the combined dry reforming of methane and catalytic decomposition of methane, the efficiency of process is strongly depended on the catalyst activity/stability, mainly caused by carbon deposition. In this study, Ni-Mo catalyst is engineered to provide a life-long performance and perform high activity in the combined process. The surface modification of catalysts by a controlled carburization pretreatment is proposed for the first time to produce a carbide catalyst along with improving the catalyst stability as well as the reactivity for direct conversion of biogas. The performance of as-prepared carbide catalysts is investigated with comparison to the oxide and metallic ones. As a result, the Ni-Mo2C catalyst exhibited superior activity and stability over its counterparts, even though the condensed nanocarbon was largely grown and covered on the surface. In addition, up to 82% of CH4 conversion and 93% of CO2 conversion could remain almost constant at 800 °C throughout the entire test period of 3 h under a high flowrate inlet stream of pure biogas at 48,000 cm3 g-1 h-1. The XPS spectra of catalysts confirmed that the presence of Mo2C species on the catalyst surface could promote the stability and reactivity of the catalyst, resulting in higher productivity of carbon nanotubes over a longer time.

Stability and Activity of Rhodium Promoted Nickel-Based Catalysts in Dry Reforming of Methane

The rhodium oxide (Rh₂O₃) doping effect on the activity and stability of nickel catalysts supported over yttria-stabilized zirconia was examined in dry reforming of methane (DRM) by using a tubular reactor, operated at 800 °C. The catalysts were characterized by using several techniques including nitrogen physisorption, X-ray diffraction, transmission electron microscopy, H₂-temperature programmed reduction, CO₂-temperature programmed Desorption, and temperature gravimetric analysis (TGA). The morphology of Ni-YZr was not affected by the addition of Rh₂O₃. However, it facilitated the activation of the catalysts and reduced the catalyst's surface basicity. The addition of 4.0 wt.% Rh₂O₃ gave the optimum conversions of CH₄ and CO₂ of ~89% and ~92%, respectively. Furthermore, the incorporation of Rh₂O₃, in the range of 0.0-4.0 wt.% loading, enhanced DRM and decreased the impact of reverse water gas shift, as inferred by the thermodynamics analysis. TGA revealed that the addition of Rh₂O₃ diminished the carbon formation on the spent catalysts, and hence, boosted the stability, owing to the potential of rhodium for carbon oxidation through gasification reactions. The 4.0 wt.% Rh₂O₃ loading gave a 12.5% weight loss of carbon. The TEM images displayed filamentous carbon, confirming the TGA results.

Plasma-Catalytic Reforming of Naphthalene and Toluene as Biomass Tar over Honeycomb Catalysts in a Gliding Arc Reactor

Biomass gasification is a promising and sustainable process to produce renewable and CO2-neutral syngas (H2 and CO). However, the contamination of syngas with tar is one of the major challenges to limit the deployment of biomass gasification on a commercial scale. Here, we propose a hybrid plasma-catalytic system for steam reforming of tar compounds over honeycomb-based catalysts in a gliding arc discharge (GAD) reactor. The reaction performances were evaluated using the blank substrate and coated catalytic materials (γ-Al2O3 and Ni/γ-Al2O3). Compared with the plasma alone process, introducing the honeycomb materials in GAD prolonged the residence time of reactant molecules for collision with plasma reactive species to promote their conversions. The presence of Ni/γ-Al2O3 gave the best performance with the high conversion of toluene (86.3%) and naphthalene (75.5%) and yield of H2 (35.0%) and CO (49.1%), while greatly inhibiting the formation of byproducts. The corresponding highest overall energy efficiency of 50.9 g/kWh was achieved, which was 35.4% higher than that in the plasma alone process. Characterization of the used catalyst and long-term running indicated that the honeycomb material coated with Ni/γ-Al2O3 had strong carbon resistance and excellent stability. The superior catalytic performance of Ni/γ-Al2O3 can be mainly ascribed to the large specific surface area and the in situ reduction of nickel oxide species in the reaction process, which promoted the interaction between plasma reactive species and catalysts and generated the plasma-catalysis synergy.

Effect of Support on Stability and Coke Resistance of Ni-Based Catalyst in Combined Steam and CO2 Reforming of CH4

Ni-based catalysts dispersed on different supports (MgO-α-Al₂O₃, CeO₂, SBA-15, and MgO-SBA-15) were prepared by the impregnation method. Characteristics of the catalysts, including specific surface areas (N₂ physisorption), crystalline phase compositions (powder X-ray diffraction, Raman spectroscopy), reducibility (hydrogen temperature-programmed reduction, H₂-TPR), and morphology (scanning electron microscopy (SEM) and transmission electron microscopy, TEM)) were investigated. The activity and stability of the catalysts were tested for the combined steam and CO₂ reforming of methane at 700 °C in a microflow system. The results show that the catalysts exhibit high activity in the BRM reaction. At 700 °C, the conversion of CH₄ and CO₂ reached 86-99% and 67-80%, respectively, in which the Ni/Mg-SBA catalyst is the best with conversions of CH₄ and CO₂ reaching 99% and 80%. Coke accumulation on the surface of the catalysts for 100 h time on stream (TOS) was evaluated by the temperature-programmed oxidation (TPO) technique. The major cause of the catalytic deactivation was elucidated by combining the determination of the amount and type of deposited coke with the changes in the physicochemical properties of the catalysts after the long-term reaction. Almost complete loss of activity was observed on Ni/Mg-Al catalyst after 100 h TOS, while the activity drop was slow on the Ni/Mg-SBA sample, about 15-20% of the total value. Otherwise, the Ni/CeO₂ and Ni/SBA catalysts firmly retained their stable activity for 100 h TOS due to the minimal carbon deposition and stability of these catalysts' structure. The highly considerable formation of inert C_γ carbon and sintering over Ni catalyst supported on MgO-α-Al₂O₃ were responsible for the lower stability of this catalyst compared to those supported on CeO₂ and SBA-15.

The Role of Strontium in CeNiO3 Nano-Crystalline Perovskites for Greenhouse Gas Mitigation to Produce Syngas

The transition metal-based catalysts for the elimination of greenhouse gases via methane reforming using carbon dioxide are directly or indirectly associated with their distinguishing characteristics such as well-dispersed metal nanoparticles, a higher number of reducible species, suitable metal–support interaction, and high specific surface area. This work presents the insight into catalytic performance as well as catalyst stability of Ce_xSr_1−xNiO₃ (x = 0.6–1) nanocrystalline perovskites for the production of hydrogen via methane reforming using carbon dioxide. Strontium incorporation enhances specific surface area, the number of reducible species, and nickel dispersion. The catalytic performance results show that CeNiO₃ demonstrated higher initial CH₄ (54.3%) and CO₂ (64.8%) conversions, which dropped down to 13.1 and 19.2% (CH₄ conversions) and 26.3 and 32.5% (CO₂ conversions) for Ce_0.8Sr_0.2NiO₃ and Ce_0.6Sr_0.4NiO₃, respectively. This drop in catalytic conversions post strontium addition is concomitant with strontium carbonate covering nickel active sites. Moreover, from the durability results, it is obvious that CeNiO₃ exhibited deactivation, whereas no deactivation was observed for Ce_0.8Sr_0.2NiO₃ and Ce_0.6Sr_0.4NiO₃. Carbon deposition during the reaction is mainly responsible for catalyst deactivation, and this is further established by characterizing spent catalysts.

Recent Advances in the Applications of Mesoporous Silica in Heterogenous Catalysis

Mesoporous silica is a class of silica material with a large specific surface area, high specific pore volume and meso-sized pores. These properties make mesoporous silica a good choice of...

A coupling bimetallic Ni–La/MCM-41 catalyst enhanced by radio frequency (RF) plasma for dry reforming

Ni–La–Imp–P exhibited excellent stability and less carbon deposition (only 5.94%) after reacting at 700 °C for 20 h.

Contribution of Oxide Supports in Nickel-Based Catalytic Elimination of Greenhouse Gases and Generation of Syngas

Carbon dioxide and/or dry methane reforming serves as an effective pathway to mitigate these greenhouse gases. This work evaluates different oxide supports including alumina, Y-zeolite and H-ZSM-5 zeolite for the catalysis of dry reforming methane with Nickel (Ni). The composite catalysts were prepared by impregnating the supports with Ni (5%) and followed by calcination. The zeolite supported catalysts exhibited more reducibility and basicity compared to the alumina supported catalysts, this was assessed with temperature programmed reduction using hydrogen and desorption using carbon dioxide. The catalytic activity, in terms of CH4 conversion, indicated that 5 wt% Ni supported on alumina exhibited higher CH4 conversion (80.5%) than when supported on Y-zeolite (71.8%) or H-ZSM-5 (78.5%). In contrast, the H-ZSM-5 catalyst led to higher CO2 conversion (87.3%) than Y-zeolite (68.4%) and alumina (83.9%) supported catalysts. The stability tests for 9 h time-on-stream showed that Ni supported with H-ZSM-5 had less deactivation (just 2%) due to carbon deposition. The characterization of spent catalysts using temperature programmed oxidation (O2-TPO), X-ray diffraction (XRD) and thermo-gravimetric analysis (TGA) revealed that carbon deposition was a main cause of deactivation and that it occurred in the lowest degree on the Ni H-ZSM-5 catalyst.

Syngas Production via CO2 Reforming of Methane over SrNiO3 and CeNiO3 Perovskites

The development of a transition-metal-based catalyst with concomitant high activity and stability due to its distinguishing characteristics, yielding an abundance of active sites, is considered to be the bottleneck for the dry reforming of methane (DRM). This work presents the catalytic activity and durability of SrNiO3 and CeNiO3 perovskites for syngas production via DRM. CeNiO3 exhibits a higher specific surface area, pore volume, number of reducible species, and nickel dispersion when compared to SrNiO3. The catalytic activity results demonstrate higher CH4 (54.3%) and CO2 (64.8%) conversions for CeNiO3, compared to 22% (CH4 conversion) and 34.7% (CO2 conversion) for SrNiO3. The decrease in catalytic activity after replacing cerium with strontium is attributed to a decrease in specific surface area and pore volume, and nickel active sites covered with strontium carbonate. The stability results reveal the deactivation of both the catalysts (SrNiO3 and CeNiO3) but SrNiO3 showed more deactivation than CeNiO3, as demonstrated by deactivation factors. The catalyst deactivation is mainly attributed to carbon deposition and these findings are verified by characterizing the spent catalysts.

Smart Designs of Anti-Coking and Anti-Sintering Ni-Based Catalysts for Dry Reforming of Methane: A Recent Review

Dry reforming of methane (DRM) reaction has drawn much interest due to the reduction of greenhouse gases and production of syngas. Coking and sintering have hindered the large-scale operations of Ni-based catalysts in DRM reactions at high temperatures. Smart designs of Ni-based catalysts are comprehensively summarized in fourth aspects: surface regulation, oxygen defects, interfacial engineering, and structural optimization. In each part, details of the designs and anti-deactivation mechanisms are elucidated, followed by a summary of the main points and the recommended strategies to improve the catalytic performance, energy efficiency, and utilization rate.

Designing Nanoparticles and Nanoalloys for Gas-Phase Catalysis with Controlled Surface Reactivity Using Colloidal Synthesis and Atomic Layer Deposition

Supported nanoparticles are commonly applied in heterogeneous catalysis. The catalytic performance of these solid catalysts is, for a given support, dependent on the nanoparticle size, shape, and composition, thus necessitating synthesis techniques that allow for preparing these materials with fine control over those properties. Such control can be exploited to deconvolute their effects on the catalyst's performance, which is the basis for knowledge-driven catalyst design. In this regard, bottom-up synthesis procedures based on colloidal chemistry or atomic layer deposition (ALD) have proven successful in achieving the desired level of control for a variety of fundamental studies. This review aims to give an account of recent progress made in the two aforementioned synthesis techniques for the application of controlled catalytic materials in gas-phase catalysis. For each technique, the focus goes to mono- and bimetallic materials, as well as to recent efforts in enhancing their performance by embedding colloidal templates in porous oxide phases or by the deposition of oxide overlayers via ALD. As a recent extension to the latter, the concept of area-selective ALD for advanced atomic-scale catalyst design is discussed.

Recent Progresses in Constructing the Highly Efficient Ni Based Catalysts With Advanced Low-Temperature Activity Toward CO2 Methanation

With the development and prosperity of the global economy, the emission of carbon dioxide (CO2) has become an increasing concern. Its greenhouse effect will cause serious environmental problems, such as the global warming and climate change. Therefore, the worldwide scientists have devoted great efforts to control CO2 emissions through various strategies, such as capture, resource utilization, sequestration, etc. Among these, the catalytic conversion of CO2 to methane is considered as one of the most efficient routes for resource utilization of CO2 owing to the mild reaction conditions and simple reaction device. Pioneer thermodynamic studies have revealed that low reaction temperature is beneficial to the high catalytic activity and CH4 selectivity. However, the low temperature will be adverse to the enhancement of the reaction rate due to kinetic barrier for the activation of CO2. Therefore, the invention of highly efficient catalysts with promising low temperature activities toward CO2 methanation reaction is the key solution. The Ni based catalysts have been widely investigated as the catalysts toward CO2 methanation due to their low cost and excellent catalytic performances. However, the Ni based catalysts usually perform poor low-temperature activities and stabilities. Therefore, the development of highly efficient Ni based catalysts with excellent low-temperature catalytic performances has become the research focus as well as challenge in this field. Therefore, we summarized the recent research progresses of constructing highly efficient Ni based catalysts toward CO2 methanation in this review. Specifically, the strategies on how to enhance the catalytic performances of the Ni based catalysts have been carefully reviewed, which include various influencing factors, such as catalytic supports, catalytic auxiliaries and dopants, the fabrication methods, reaction conditions, etc. Finally, the future development trend of the Ni based catalysts is also prospected, which will be helpful to the design and fabrication of the Ni catalysts with high efficiency toward CO2 methanation process.

Gas-Permeable Inorganic Shell Improves the Coking Stability and Electrochemical Reactivity of Pt toward Methane Oxidation

Solid oxide fuel cells produce electricity directly by oxidizing methane, which is the most attractive natural gas fuel, and metal nanocatalysts are a promising means of overcoming the poor catalytic activity of conventional ceramic electrodes. However, the lack of thermal and chemical stability of nanocatalysts is a major bottleneck in the effort to ensure the lifetime of metal-decorated electrodes for methane oxidation. Here, for the first time, this issue is addressed by encapsulating metal nanoparticles with gas-permeable inorganic shells. Pt particles approximately 10 nm in size are dispersed on the surface of a porous La_0.75Sr_0.25Cr_0.5Mn_0.5O₃ (LSCM) electrode via wet infiltration and are then coated with an ultrathin Al₂O₃ layer via atomic layer deposition. The Al₂O₃ overcoat, despite being an insulator, significantly enhances the immunity to carbon coking and provides high activity for the electrochemical oxidation of methane, thereby reducing the reaction impedance of the Pt-decorated electrode by more than 2 orders of magnitude and making the electrode activity of the Pt-decorated sample at 650 °C comparable with those reported at 800 °C for pristine LSCM electrodes. These observations provide a new perspective on strategies to lower the operation temperature, which has long been a challenge related to hydrocarbon-fueled solid oxide fuel cells.

Catalytic Activity of Nickel and Ruthenium–Nickel Catalysts Supported on SiO2, ZrO2, Al2O3, and MgAl2O4 in a Dry Reforming Process

Dry reforming of methane (DRM) is an eco-friendly method of syngas production due to the utilization of two main greenhouse gases—methane and carbon dioxide. An industrial application of methane dry reforming requires the use of a catalyst with high activity, stability over a long time, and the ability to catalyze a reaction, leading to the needed a hydrogen/carbon monoxide ratio. Thus, the aim of the study was to investigate the effect of support and noble metal particles on catalytic activity, stability, and selectivity in the dry reforming process. Ni and Ni–Ru based catalysts were prepared via impregnation and precipitation methods on SiO2, ZrO2, Al2O3, and MgAl2O4 supports. The obtained catalysts were characterized using X-ray diffractometry (XRD), inductively coupled plasma optical emission spectrometry (ICP-OES), Brunauer–Emmett–Teller (BET) specific surface area, and elemental carbon-hydrogen-nitrogen-sulphur analysis (CHNS) techniques. The catalytic activity was investigated in the carbon dioxide reforming of a methane process at 800 °C. Catalysts supported on commercial Al2O3 and spinel MgAl2O4 exhibited the highest activity and stability under DRM conditions. The obtained results clearly indicate that differences in catalytic activity result from the dispersion, size of an active metal (AM), and interactions of the AM with the support. It was also found that the addition of ruthenium particles enhanced the methane conversion and shifted the H2/CO ratio to lower values.

Catalytic Behaviour of Ce-Doped Ni Systems Supported on Stabilized Zirconia under Dry Reforming Conditions

Ni supported on bare and modified ZrO2 samples were synthesized using the incipient wet impregnation method. The t-ZrO2 phase was stabilized by incorporation of La2O3 into ZrO2. Moreover, the influence of CeO2-doping on the physico-chemical and catalytic properties under CO2 reforming conditions was probed. The characterization data of the investigated catalysts were obtained by using XRD, CO2/H2-TPD, BET, TPR, TPO, TGA, XPS and TEM characterization techniques. In the pristine Ni/Zr catalyst, the t-ZrO2 phase transformed into the monoclinic phase. However, upon support modification by La2O3, significant effects on the physicochemical properties were observed due to the monoclinic-to-tetragonal ZrO2 phase transformation also affecting the catalytic activity. As a result, superior activity on the La2O3 modified Ni/Zr catalyst was achieved, while no relevant change in the surface properties and activity of the catalysts was detected after doping by CeO2. The peculiar behavior of the Ni/La-ZrO2 sample was related to higher dispersion of the active phase, with a more pronounced stabilization of the t-ZrO2 phase.

Nanosized Ni/SBA-15 Catalysts for CO2 Reforming of CH4

Ni, Co, and Co–Ni bimetallic catalysts supported over SBA-15 and over SBA-15 doped with Zn or Ce oxides were prepared and tested in a methane dry reforming reaction. The loading of the metals in the catalyst was 5 wt % for either mono or bimetallic catalysts. The prepared catalysts were tested in a continuous-flow fixed-bed reactor at 800 °C under atmospheric pressure. XRD, TPR, TPD, and SEM characterization techniques were employed to investigate the catalytic properties of fresh catalysts. SEM and TGA were used to study the catalytic properties of spent catalysts. A remarkable effect on the reduction properties and catalytic performance of catalysts was observed after adding Zn and Ce. Over an 8 h test, Ni/SBA-15 showed the best activity and stability. The conversion was 90% for CH4 and CO2. Co–Ni/SBA-15 and Co–Ni/Ce–SBA-15 have shown a reasonable activity and stability. Selectivity of the Ni/SBA-15 catalyst was higher than all other catalysts as indicated by the H2/CO ratio. Co/SBA-15 and Co–Ni/Zn–SBA-15 showed a low activity and selectivity. TPD–NH3 profiles indicated that doping SBA-15 with Ce and/or Zn increased the catalyst acidic sites. Ni/SBA-15 is an excellent potential catalyst for commercial methane dry reforming processes.

Highly Selective Syngas/H2 Production via Partial Oxidation of CH4 Using (Ni, Co and Ni–Co)/ZrO2–Al2O3 Catalysts: Influence of Calcination Temperature

In this study, Ni, Co and Ni–Co catalysts supported on binary oxide ZrO2–Al2O3 were synthesized by sol-gel method and characterized by means of various analytical techniques such as XRD, BET, TPR, TPD, TGA, SEM, and TEM. This catalytic system was then tested for syngas respective H2 production via partial oxidation of methane at 700 °C and 800 °C. The influence of calcination temperatures was studied and their impact on catalytic activity and stability was evaluated. It was observed that increasing the calcination temperature from 550 °C to 800 °C and addition of ZrO2 to Al2O3 enhances Ni metal-support interaction. This increases the catalytic activity and sintering resistance. Furthermore, ZrO2 provides higher oxygen storage capacity and stronger Lewis basicity which contributed to coke suppression, eventually leading to a more stable catalyst. It was also observed that, contrary to bimetallic catalysts, monometallic catalysts exhibit higher activity with higher calcination temperature. At the same time, Co and Ni–Co-based catalysts exhibit higher activity than Ni-based catalysts which was not expected. The Co-based catalyst calcined at 800 °C demonstrated excellent stability over 24 h on stream. In general, all catalysts demonstrated high CH4 conversion and exceptionally high selectivity to H2 (~98%) at 700 °C.

Synthesis and Properties of SBA-15 Modified with Non-Noble Metals

Modification of SBA-15 with non-noble metal leads to functional materials, which can be applied as gas sensors, adsorbents, and catalysts of various reactions. The new materials contain up to four various metals, which are deposited consecutively or simultaneously at various concentrations ranging from a fraction of 1% to an amount that is comparable with the mass of silica-support. These materials contain metals at various oxidation levels, usually as oxides, which occur in crystalline form (a typical crystallite size of about 10 nm matches the width of the SBA-15 channels), but in a few other materials, crystalline metal compounds have not been detected. Many researchers have provided detailed physico- chemical characteristics of SBA-15 modified with non-noble metals by the means of various microscopic and spectroscopic techniques.

Silica-based micro- and mesoporous catalysts for dry reforming of methane

With wide availability, high thermal stability and high specific surface area, silica-based micro- and mesoporous materials show promising performance for dry reforming of methane reaction, boosting efficient and sustainable utilization of greenhouse gases.