Ziwei Li

Progress in Synthesis of Highly Active and Stable Nickel‐Based Catalysts for Carbon Dioxide Reforming of Methane

In recent decades, rising anthropogenic greenhouse gas emissions (mainly CO2 and CH4 ) have increased alarm due to escalating effects of global warming. The dry carbon dioxide reforming of methane (DRM) reaction is a sustainable way to utilize these notorious greenhouse gases. This paper presents a review of recent progress in the development of nickel-based catalysts for the DRM reaction. The enviable low cost and wide availability of nickel compared with noble metals is the main reason for persistent research efforts in optimizing the synthesis of nickel-based catalysts. Important catalyst features for the rational design of a coke-resistant nickel-based nanocatalyst for the DRM reaction are also discussed. In addition, several innovative developments based on salient features for the stabilization of nickel nanocatalysts through various means (which include functionalization with precursors, synthesis by plasma treatment, stabilization/confinement on mesoporous/microporous/carbon supports, and the formation of metal oxides) are highlighted. The final part of this review covers major issues and proposed improvement strategies pertaining to the rational design of nickel-based catalysts with high activity and stability for the DRM reaction.

Simultaneous Tuning Porosity and Basicity of Nickel@Nickel–Magnesium Phyllosilicate Core–Shell Catalysts for CO2 Reforming of CH4

Ni@Ni-Mgphy (Ni-Mgphy = Ni-Mg phyllosilicate) core-shell catalysts were designed by hydrothermally treating Ni@SiO2 nanoparticles with magnesium nitrate salt. The porosity and basicity of the catalysts were easily tuned by forming Ni-Mgphy shell using Ni originating from Ni@SiO2 during the hydrothermal treatment process and Mg(NO3)2 as the Ni and Mg sources, respectively. Among Ni@Ni-Mgphy core-shell catalysts synthesized under different hydrothermal durations, the catalyst treated for 10 h achieved the best catalytic performance for CO2 reforming of CH4 reaction with stable CO2 and CH4 conversions of around 81% and 78%, respectively, within 95 h reaction duration at 700 °C. The high Ni accessibility, strong basicity, and high structural stability for Ni@Ni-Mgphy core-shell catalyst with 10 h treatment time accounted for its superb catalytic performance. This method to simultaneously tune the porosity and basicity of Ni@SiO2 core-shell nanoparticles demonstrates a general way to modify the properties of other silica based core-shell nanoparticles through treating them with different metal salts.

Facile Synthesis of High Surface Area Yolk–Shell Ni@Ni Embedded SiO2 via Ni Phyllosilicate with Enhanced Performance for CO2 Reforming of CH4

Ni@Ni embedded SiO2 yolk–shell nanocomposites with controllable specific surface area are synthesized by using a facile self‐templating method via the transformation of Ni phyllosilicate (NiPhy). NiPhy is found to form initially at the interface of Ni and SiO2, stretching its branches within the whole SiO2 shell and outward onto the SiO2 surface. Upon calcination and reduction, NiPhy decomposes to smaller Ni nanoparticles within the SiO2 shell to form a Ni@Ni embedded SiO2 yolk–shell nanocomposite with high surface area, high Ni dispersion, and strong interaction between Ni and SiO2. The nanocomposite with a treatment time of 12 h exhibits stable and high CO2 and CH4 conversions of 82 and 74 %, respectively, for the CO2 reforming reaction of CH4 at 700 °C within the testing period of 50 h. This interfacial transformation method is promising for the synthesis of other Ni@NiM (M=Cu, Zn, and Mg) phyllosilicate yolk–shell nanocomposites for application as adsorbents and catalysts of other processes.

Multi-Ni@Ni phyllosilicate hollow sphere for CO2 reforming of CH4: influence of Ni precursors on structure, sintering, and carbon resistance

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.

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

The increasing environmental concern on global warming has triggered intensive research on sustainable utilization of greenhouse gases. CO2 (dry) reforming of methane (DRM) is one of the most effective means since it can transform two major greenhouse gases, CO2 and CH4, together into the more valuable synthesis gas. Silica-based micro- and mesoporous materials turned out to be one promising class of catalysts due to their wide availability, high thermal stability and high specific surface area. In this article, we have overviewed the background and key problems lying in DRM as well as the strength and weakness of silica-based materials used for DRM. Recent developments on these silica-based micro- and mesoporous catalysts including Ni-based catalysts, bimetallic catalysts, perovskite catalysts, Ni-based catalysts doped with promoters and core–shell catalysts for DRM have then been presented by summarizing the synthesis methods and reasons leading to the high catalytic performance and carbon resistance. Finally, key challenges and possible strategies to improve these silica-based catalysts for DRM have been discussed.

Sintering resistant Ni nanoparticles exclusively confined within SiO2 nanotubes for CH4 dry reforming

Confining nanoparticles within the channels of one dimensional nanotubes (1D NTs) is one of the effective measures to design sintering resistant catalysts. To achieve this goal, improving the infiltration efficiency of metal precursors into the channels of 1D NTs has been regarded as one of the key issues. Herein, a novel method has been developed to exclusively confine Ni nanoparticles within SiO2 NTs using Ni phyllosilicate (NiPhy) NTs@SiO2 core shell nanocomposites as precursors, where NiPhy NTs will in situ decompose into Ni nanoparticles within the SiO2 shell NTs upon reduction under H2 at 700 °C. Strong interactions between Ni and the SiO2 NT shell, the confinement effect and the hindrance effect provided by the SiO2 nanoparticles sitting among the Ni nanoparticles within the channel of SiO2 NTs prevent the sintering of Ni nanoparticles. These nanocomposites show good catalytic performance and carbon resistance for CO2 reforming of CH4 reaction to produce synthesis gas. This novel method can be easily applied to design other sintering resistant catalysts with exclusive confinement of other metals (M = Co, Fe, Cu etc.) within the channels of SiO2 NTs for other applications.