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Catalytic dry (CO2) reforming of plastic-derived syngas is a promising method of producing hydrogen-rich syngas and reducing greenhouse gases. The development of catalysts with high activity and stability is critical for this reaction. In this study, we fabricated core-shell structured Ni@Al2O3 catalysts with different shell thicknesses using advanced polyol and sol-gel methods. The effects of different Al/Ni ratios on the activity and stability of the catalysts in the CO2 reforming reaction were investigated. The main challenge for CO2 reforming of methane is carbon deposition. In the developed catalysts, the mesoporous Al2O3 coating outside the Ni core enhances the stability. However, the interaction between the core and the shell strongly affects the catalyst activity and product selectivity in the reaction. The catalyst with an Al/Ni ratio of 2 exhibited the highest methane conversion of up to 88% and the lowest carbon deposition, compared to the congeners with Al/Ni ratios of 1 and 3.

This study aims to develop a two-stage fluidized catalytic bed reactor system for continuous co-production of carbon nanotubes (CNTs) and hydrogen from waste plastics gasification. Ni/Al-SBA-15 and Ni–Cu/CaO–SiO2 catalysts have been synthesized and granulated for CNTs synthesis and hydrogen production in the first- and second-stage reactor, respectively. The operating parameters, including reaction temperature and equivalence ratio (ER), were investigated to confirm the feasibility for CNTs and hydrogen production of this system. The Ni/Al-SBA-15 added in the first-stage reactor enhanced the waste plastics degradation to produce CH4 and C2–C5 hydrocarbons with increasing temperature, which could be used as the source for CNTs synthesis. Lowering the ER promoted the catalytic thermal cracking and reforming of hydrocarbons that contributed to the CNTs and hydrogen production. Nevertheless, the H2 production rate showed a significant increase to 857.6 mmol/h-g catalyst with the assistance of Ni–Cu/CaO–SiO2 in the second-stage reactor. The produced smaller-molecule hydrocarbons from the second-stage reactor with higher temperatures could benefit the co-production of CNTs and hydrogen. The two-stage fluidized catalytic bed gasification system exhibited an optimal performance of high fraction CNTs and H2 when temperatures of first- and second-stage reactor were controlled at 600 and 800 °C, respectively, with 0.1 ER.

In this study, a core–shell structured catalyst composed of a nickel core coated with a high thermal-stability shell layer was prepared for the decomposition of waste plastics to produce hydrogen. Ceria–zirconia mixed metal oxide was used as the coating layer to protect the active phase of the catalyst. The as-prepared catalyst was firstly tested using a methane cracking process to evaluate its stability under high temperature and coking conditions. The special redox characteristics of the Ni@CeO2–ZrO2 core–shell-structured catalyst provide lattice oxygen to oxidize carbon produced during the reaction and extend the life of the catalyst during the coking resistance test. Different pore sizes in the functional shell were prepared by adding a templating agent, and the catalyst was tested for its ability to produce hydrogen from plastic waste. The CeO2–ZrO2 shell promoted the production of active oxygen species and enhanced the dispersion of the Ni cores, which are beneficial attributes for plastic waste decomposition.

In the present work, a core-shell structured Co/SiO2@HZSM-5 catalyst was prepared for hydrogen production from syngas of plastic waste gasification. The cobalt catalyst was coated with HZSM-5 shell through a hydrothermal process, and the Co/SiO2@HZSM-5, with different loadings of HZSM-5 (e.g., 10–30 wt %) exhibited excellent activity and durability for dehydrogenation reactions. The amount of HZSM-5 was found to be an important factor for hydrogen production. Temperature-programmed reduction with H2 and temperature-programmed desorption of ammonia was applied to determine the active site and the acidity of prepared catalyst, respectively. The prepared Co/SiO2@HZSM-5 was tested through reforming of plastic gasification syngas and shown superior hydrogen production ability (∼90%) and stability (over 15 h). The effects of reduction-oxidation behavior on the catalytic performance were also discussed.

Ni/SiO2 core–shell catalysts were prepared by deposition–precipitation method and used to produce hydrogen from waste plastics-derived syngas. The SiO2 core synthesized by the Stober process was used as the support. This core was synthesized using various solvents, and the effect of these solvents on the morphologies and catalytic performance of the Ni/SiO2 core–shell catalysts was investigated. The synthesis parameters of the Ni/SiO2 catalysts were further investigated to enhance the metal–support interaction and dispersion of Ni on the SiO2 support. The highest catalytic activity of 181 mmol/g-h was achieved when the Ni/SiO2 core–shell catalyst was synthesized in methanol (Ni/SiO2–M) and reacted at 800 °C at a water-addition rate of 0.75 g-H2O/h. The Ni/SiO2–M catalyst, which possessed strong metal–support interaction nickel phyllosilicates, high specific area, small particle size, and homogeneous metal dispersion, exhibited the best long-term stability.

The thermochemical treatment of waste plastics to produce H2-rich syngas is a promising technique for both waste management and the regeneration of valuable energy resources. In this paper, we report the synthesis of Ni@CeO2 core–shell catalyst with different shell thicknesses. The H2 production ability of the Ni@CeO2 core–shell catalysts was tested and compared to that of the supported Ni/CeO2 catalyst, and it was determined that the H2 yield of the Ni@CeO2 core–shell catalysts was significantly higher than that of the supported Ni/CeO2 catalyst. Owing to the hollow space between the core and shell providing a reacting space for heterogeneous catalysis, the amount of H2 obtained employing the Ni@CeO2-0.5 catalyst, which was obtained using 0.5 mmol cerium nitrate, was the highest of all analyzed Ni@CeO2 catalysts in this study. The optimal H2 production rate of 730.6 mmol/(h g was obtained at 700 °C when the equivalence ratio (ER) was 0.1.

A novel and simple synthetic approach toward core–shell Fe@Al2O3 nanocomposites were developed in this study. The as-synthesized catalyst was applied to convert the methane into carbon nanotubes. Moreover, due to the properties of the core–shell structure, the amount of surfactant can be adjusted to control the pore size of the shell and further control the diameter of the carbon nanotubes. In this study, the conversion of CH4 was up to 97% and the carbon production was 135 mgC/gcat.*h, which is much higher than traditional supported catalysts under similar reaction conditions. In addition, the carbon product quality (IG/ID) was up to 1.96. The enhanced CH4 catalytic activity for the core–shell Fe@Al2O3 catalyst originated from the combined acidic sites on the surface of the Al2O3 shell and the high carbon diffusion rate of the Fe core, which led to the high efficiency of CH4 conversion and longer lifetime of the catalyst.

A core-shell type catalyst was applied to convert polyethylene (PE) plastic wastes into hydrogen using a two-stage pyrolysis-catalysis reactor. The effects of catalyst: plastic ratio, reaction temperature, and the suppression of coke formation on catalytic performance were investigated. Ni-Ce bimetallic catalyst was synthesized via modified polyol method, and the silica coating with different Ni:Si molar ratio was prepared with the extension of Stober method. Different thickness of silica shell was synthesized and tested for hydrogen production from PE waste. The encapsulation of Ni-Ce core by silica shell could effectively inhibit the sintering of nanoparticles under high temperature conditions. The highest amount of hydrogen production was found when the catalyst: plastic weight ratio was 1.0, and the catalytic reaction temperature was 800 °C. The core-shell catalyst also exhibited great ability of coking resistance, showing great catalytic performance within 5 times of reuse.