Display omitted
•NiCo@NiCo phyllosilicate@CeO2 core shell hollow spheres have been designed.•They exhibit active and stable performance of 45 h TOS for STR reaction.•High metal sintering resistance ...and oxygen vacancies alleviate the carbon deposition.•Synergistic effect between Ni and Co further improves their carbon resistance.•They show promising application in tar steaming reforming reaction.
Developing sintering and carbon resistant tar removal catalysts is crucial for biomass gasification technology. Herein, for the first time, NiCo@NiCo phyllosilicate@CeO2 hollow core shell catalysts have been designed for steam reforming of toluene (SRT) as the biomass tar model compound. They show both good catalytic activity and stability within 45 h of time on stream due to their high sintering resistance of NiCo because of the strong interactions between NiCo and CeO2, high metal exposure as a result of the high specific surface area, high surface metal concentration as well as the high oxygen vacancies as evidenced from the H2-Temperature-programmed reduction (H2-TPR), H2 chemisorption and X-ray photoelectron spectroscopy (XPS) characterizations respectively. Additionally, the synergistic effect between Ni and Co further improves their carbon resistant property. By comparison, Co@Co phyllosilicate@CeO2 catalysts perform the lowest toluene conversion and stability mainly due to their structural instability during reaction resulting from their high Si/Co ratio, leading to their low specific surface area and Co exposure. The outstanding SRT performance of NiCo@NiCo phyllosilicate@CeO2 catalysts indicates their promising application for steam reforming of biomass tar reaction.
A great challenge for cheap and active Ni‐based catalysts to be utilized for CO2 (dry) reforming of methane (DRM) reaction is their high‐carbon‐deposition problem. Herein, we designed ...multi‐Ni‐core@Ni phyllosilicate@CeO2 (Ni@NiPhy@CeO2) shell hollow sphere catalysts using a facile precipitation method. Compared with Ni@NiPhy without CeO2 shell, Ni@NiPhy@CeO2 exhibits high carbon resistance for the DRM reaction at both high GHSV value of 1880 L g−1 cat h−1 at 700 °C and a low reaction temperature of 600 °C. In addition, they show high and stable CH4 and CO2 conversions of 72.8 % and 79.1 % respectively at 700 °C under normal GHSV value of 36 L g−1 cat h−1. The good catalytic performance of Ni@NiPhy@CeO2 can be attributed to their high sintering resistance of both Ni and CeO2 which yields a high concentration of oxygen vacancies thereby a high catalytic performance and carbon resistance for DRM reaction. The facile synthesis method in this work can easily be applied to design other core–shell hollow catalysts such as Ni–M (M=Mg, Co, Cu, and Fe) silicate@CeO2 according to specific applications.
Hollow spheres for dry reforming: Multi‐Ni@Ni phyllosilicate@CeO2 core–shell hollow spheres with high sintering resistance of both Ni and CeO2 are synthesized using a facile precipitation method, yielding high concentration of oxygen vacancies that leads to high catalytic performance and carbon resistance for the CH4 dry reforming reaction.
We synthesize a new sandwich‐like silica@Ni@silica multicore–shell catalyst. Firstly, Ni phyllosilicate (NiPS) is supported on silica nanospheres by a simple ammonia evaporation method. Then NiPS is ...coated with a layer of mesoporous silica to obtain a core–shell NiPS@silica structure by the hydrolysis of tetraethylorthosilicate (TEOS). The thickness of the shell can be tuned by varying the amount of TEOS. After calcination and H2 reduction at high temperature, multiple small Ni nanoparticles (≈6 nm) are generated and supported on the inner silica core but also encapsulated within the outer mesoporous silica shell. This silica@Ni@silica multicore–shell catalyst shows a high and stable conversion (≈60 %, gas hourly space velocity=60 000 mL h−1 gcat−1) for the dry reforming of methane (DRM) at 600 °C, whereas pristine NiPS deactivates quickly because of heavy carbon formation. We investigated the spent catalysts by using thermogravimetric analysis and TEM and found that there is almost no carbon formation for this new multicore–shell catalyst. Compared with a conventional Ni@silica core–shell catalyst, our multicore–shell catalyst is much easier to synthesize and the process does not require any toxic organic solvents. We believe that this strategy to make a multicore–shell catalyst can be applied to more nanomaterials and extended to other catalytic reactions besides DRM.
Resistance is useful: A new sandwich‐like silica@Ni@silica multicore–shell catalyst is prepared. This catalyst shows a stable catalytic performance and high carbon resistance for the low‐temperature dry reforming of methane because of the confinement effect.
Display omitted
•Calcium-looping dry reforming of methane is achieved at moderate temperature.•Ni/CaO-CeO2 microsphere is developed for isothermal CO2 capture and in-situ conversion.•Homogeneously ...mixed CeO2 serves as both structure stabilizer and activity promoter.•Fast CaCO3 decomposition and high reforming activity leads to high syngas yield.
Efficient integration of calcium-looping (CaL) and dry reforming of methane (DRM), termed as CaLDRM, into an isothermal process implemented on a bifunctional Ni-CaO based material is a promising technology to achieve CO2 capture and in-situ conversion to syngas, thereby allowing a win–win for environment and economy. The core of this technology is the employed material which should ensure both good CO2 capture capacity and significant catalytic activity at a temperature matching CaL and DRM. To this end, we synthesize a Ni supported porous CeO2-modified CaO microsphere to serve as the bifunctional material by a combination of template-assisted hydrothermal and impregnation method. This material successfully drives cyclic CO2 capture and conversion at the same temperature of 650 °C, i.e. simultaneously realizing high-temperature CaL and low-temperature DRM. The role of Ce on boosting the material performance originates from two aspects: on the one hand, the homogeneously mixed CeO2, as an activity promoter, enhances the CO2 affinity of CaO and the low-temperature activity of Ni, enabling higher CO2 capture and conversion capacities at 650 °C; on the other hand, it, as a structure stabilizer, improves the sinter resistance of CaO and the dispersion of Ni, maintaining the CaL kinetics and catalytic DRM activity. Following the premise of minimizing additive quantity, the bifunctional material constructed from the support with a Ca:Ce molar ratio of 85:15 shows stable CO2 uptake and syngas yield during the isothermal CaLDRM cycles at 650 °C, exceeding the performance of unmodified material by more than 2 times.
Display omitted
•CO2 conversion to fuels such as methane.•Strategic development of catalyst for CO2 conversion.•Process intensification via catalytic membrane processes.•Energy efficient methanation ...via plasma-assisted catalysis process.•Green methane synthesis via photo-catalytic process.
This review focuses on various catalytic CO2 hydrogenation approaches for converting CO2 to fuels such as CH4. The catalytic CO2 methanation using thermal, catalytic-membrane, photo and plasma energy assisted processes were covered. The recent catalysts developments in thermo-catalytic systems for CO2 methanation in thermal process with respect to the nature of active catalytic centres and their performance were presented. Followed by the technological development of catalytic-membrane process and its advantages in overcoming thermodynamic equilibrium activities were also discussed. Additionally, the catalytic CO2 hydrogenation process assisted with plasma and photo energy were also covered with respect to the catalyst structures, CO2 conversion and selectivity towards various products. Several highly emerging in situ characterization techniques such as operando XAS and DRIFTS were used to understand the state of catalyst surface and reaction intermediates involved in CO2 methanation reaction. Furthermore, parameters affecting the selectivity towards desired products and methods to improve the performance are explained in greater details. Finally, a section for technological challenges of CO2 methanation in various processes are summarized and an outlook for future directions of the development of catalysts was provided to overcome the CO2 conversion and selectivity towards desired products limitations to eradicate the problems associated with global warming.
Multi-Ni@Ni phyllosilicate hollow spheres (NiPhy HS) were synthesized using different Ni precursors via hydrothermal and H2 reduction methods. Precursor effects to the NiPhy HS structure and ...catalytic performance for CO2 (dry) reforming of the CH4 (DRM) reaction were investigated and established. Ni@NiPhy-(Ac)2 achieved near equilibrium conversions with negligible carbon formation for the DRM reaction at 700 °C. The structure of NiPhy HS was influenced by different nickel precursors because Ni ions with different sizes were produced leading to their relatively different diffusion speeds through the previously formed NiPhy layer to further react with the silicate ions near the unreacted silica surface in the core part to form the new NiPhy phases. The unique pore structure with smallest pore size and pore volume for NiPhy-(Ac)2 compared with NiPhy-OAc and NiPhy-NO3 contributes to eliminating the deposition of carbon species due to the confinement effect. In addition, the strongest interaction between Ni and NiPhy phases for NiPhy-(Ac)2 inhibits the sintering of Ni nanoparticles and prevents the lifting away of Ni from NiPhy phases by the deposited carbon species thereby retarding the growth of carbon nanotubes. This study demonstrates a method to design other metal (M = Co, Fe, and Cu) phyllosilicate nano-hollow spheres with high metal loading as high sintering and carbon resistant catalysts for other catalytic applications.
Catalytic conversion of CO2 to produce fuels and chemicals is attractive in prospect because it provides an alternative to fossil feedstocks and the benefit of converting and cycling the greenhouse ...gas CO2 on a large scale. In today's technology, CO2 is converted into hydrocarbon fuels in Fischer–Tropsch synthesis via the water gas shift reaction, but processes for direct conversion of CO2 to fuels and chemicals such as methane, methanol, and C2+ hydrocarbons or syngas are still far from large-scale applications because of processing challenges that may be best addressed by the discovery of improved catalysts—those with enhanced activity, selectivity, and stability. Core–shell structured catalysts are a relatively new class of nanomaterials that allow a controlled integration of the functions of complementary materials with optimised compositions and morphologies. For CO2 conversion, core–shell catalysts can provide distinctive advantages by addressing challenges such as catalyst sintering and activity loss in CO2 reforming processes, insufficient product selectivity in thermocatalytic CO2 hydrogenation, and low efficiency and selectivity in photocatalytic and electrocatalytic CO2 hydrogenation. In the preceding decade, substantial progress has been made in the synthesis, characterization, and evaluation of core–shell catalysts for such potential applications. Nonetheless, challenges remain in the discovery of inexpensive, robust, regenerable catalysts in this class. This review provides an in-depth assessment of these materials for the thermocatalytic, photocatalytic, and electrocatalytic conversion of CO2 into synthesis gas and valuable hydrocarbons.
In recent years, CO2 reforming of methane (dry reforming of methane, DRM) has become an attractive research area because it converts two major greenhouse gasses into syngas (CO and H2), which can be ...directly used as fuel or feedstock for the chemical industry. Ni‐based catalysts have been extensively used for DRM because of its low cost and good activity. A major concern with Ni‐based catalysts in DRM is severe carbon deposition leading to catalyst deactivation, and a lot of effort has been put into the design and synthesis of stable Ni catalysts with high carbon resistance. One effective and practical strategy is to introduce a second metal to obtain bimetallic Ni‐based catalysts. The synergistic effect between Ni and the second metal has been shown to increase the carbon resistance of the catalyst significantly. In this review, a detailed discussion on the development of bimetallic Ni‐based catalysts for DRM including nickel alloyed with noble metals (Pt, Ru, Ir etc.) and transition metals (Co, Fe, Cu) is presented. Special emphasis has been provided on the underlying principles that lead to synergistic effects and enhance catalyst performance. Finally, an outlook is presented for the future development of Ni‐based bimetallic catalysts.
Allied alloys: In this review, a detailed discussion on the development of bimetallic Ni‐based catalysts for dry reforming of methane (DRM) including nickel alloyed with noble metals (Pt, Ru, Ir etc.) and transition metals (Co, Fe, Cu) is presented. Special emphasis is placed on the underlying principles that lead to synergistic effects and enhance catalyst performance. Finally, an outlook is presented for future development of Ni‐based bimetallic catalysts.
Plasma-catalytic direct nonoxidative coupling of methane (NCM) into C2 hydrocarbons was investigated over ceria-supported atomically dispersed Pt (Pt/CeO2-SAC) and nanoparticle Pt (Pt/CeO2-NP) ...catalysts in dielectric barrier discharge (DBD) plasma. Nonthermal plasma facilitated C–H bond dissociation in CH4 at low temperatures (<150 °C) and atmospheric pressure. The presence of Pt/CeO2 catalysts in plasma further enhanced CH4 conversion and C2 hydrocarbon selectivity by enabling the conversion of vibrationally excited methane species with high internal energy on active Pt sites. Noticeably, the Pt/CeO2-SAC catalyst displayed a more remarkable performance, with a CH4 conversion of 39% and a C2 selectivity of 54% at 54 W. The enhanced CH4 conversion was attributed to abundant coordinatively unsaturated Pt sites in Pt/CeO2-SAC, which were more active for C–H bond scission. Meanwhile, isolated Pt atoms in Pt/CeO2-SAC promoted C2 hydrocarbon formation by hindering the unselective formation of coke from deep dehydrogenation of CH x • intermediates and higher hydrocarbons from oligomerization reactions.
PDF
