Preparation, modification, and characterisation of Yolk-shell structure based catalysts for synthetic gas production

Hydrogen is an emerging energy carrier for oil refining and fuel cell applications. The development of an efficient and stable catalyst to produce hydrogen gas is required for industrial applications. However critical issues in the catalyst that lead to the deactivation of reactions include active metal particle growth and carbon fouling. Industrial catalysts that are frequently overwhelmed by such issues are substituted or re-treated, which is not time and cost efficient. Therefore, developing durable catalysts that are resistant to sintering and carbon fouling remains an area of interest. A novel and anti-agglomeration Ni@yolk-ZrO2 catalyst is first reported in this thesis. A specific study of the ZrO2 hollow shell showed that the varied porosity of the hollow shell contributed to the catalyst’s ability to inhibit the agglomeration of active Ni particles. The steam reforming of methane was selected as the probe study for this catalyst in this research. Before a thorough analysis of the Ni@yolk-ZrO2 catalyst was performed, the systematic synthesis of Ni@SiO2 was studied. The analysis showed that the Ni particle size can be controlled by tuning the synthesis temperature. Water-to-surfactant ratio in the microemulsion was shown to influence the morphology of the Ni@SiO2 particle. The tetraethyl orthosilicate (TEOS) amount added with fractionated dispensing and the amount of NiCl2 were found to have affected the size and morphology of the Ni@SiO2. For the Ni@yolk-ZrO2 sample, the catalyst was characterised by Transmission Electron Microscopy (TEM) and X-Ray Diffraction. TEM was used for morphology analysis, while X-ray Diffraction was performed for phase analysis and crystallite size measurements. Nitrogen adsorption-desorption isotherm was done to measure specific surface area, total pore volume, and the t-plot micropore volume of the samples. Reducibility analysis of the Nickel species of the Ni@yolk-ZrO2 catalyst was carried out using Temperature Programmed Reduction. The anti-agglomeration property of the Ni@yolk-ZrO2 was established from the TEM and X-ray Photoelectron Spectroscopy analysis. Results showed that the active Ni particles were inside the yolk-shell structured framework, which deterred Ni particles from moving onto the surface of the catalyst. Ni particles were found to be stabilised by the abundant volume of pores in the ZrO2 hollow shell. This result indicates that the Ni particles were anchored by the pores and remained stable during the steam reforming of methane. The Ni@yolk-ZrO2 catalyst was tested by varying the volumes of feed (GHSV) and the steam-to-carbon ratio. This catalyst was also subjected to a recyclability test and proved to be better than conventional impregnated Ni/ZrO2 catalysts. The Temperature Programmed Hydrogenation analysis also proofed that the yolk-shell structure framework inhibited higher order of carbon deposits on the Ni@yolk-ZrO2 catalyst. Varying the porosity of the ZrO2 hollow shell was found to affect the performance of the steam reforming of methane. This varied porosity can be achieved by varying the amount of surfactant during the synthesis of Ni@SiO2@ZrO2. X-ray Photoelectron Spectroscopy analysis results showed that the porosity of the ZrO2 hollow shell contributed to the moderately strong hydrothermal stability of the catalyst for the steam reforming of methane. The hollow shell of the ZrO2 was influenced by the instability of the SiO2. TEM analysis of used BrNi-4.8 catalysts showed that the yolk-shell structure framework of the catalyst collapsed. This result suggests that the shell has weak integrity, and proves that the SiO2 was not able to maintain the yolk-shell framework. The results also suggest that the varied porosity of the ZrO2 hollow shell influences the catalysts’ efficiency even though they share the same yolk-shell structure framework. This is likely due to the differences in the pores of each catalyst configuration, which directly affects the Nickel species involved in the catalytic reaction. Finally, it was demonstrated that the Ni@yolk-ZrO2 catalyst exhibits excellent catalytic performance in comparison to conventional catalysts for the steam reforming of methane. Catalytic activity remained stable and achieved a methane conversion of more than 90 % for 150 hours under operating conditions of GHSV of 50400 mL gcat-1h-1 and S/C = 2.5 at 750 oC

A novel and anti-agglomerating Ni@yolk–ZrO₂ structure with sub-10 nm Ni core for high performance steam reforming of methane

Steam reforming of methane is a versatile technology for hydrogen production in oil refinery and fuel cell applications. Using natural gas is a promising method to produce rich-hydrogen gas. Ni@yolk–ZrO₂ catalyst is used to study steam reforming of methane under various GHSVs, steam-to-carbon (S/C) ratio, and its recyclability. The catalyst was characterized using a combination of XRD, TEM, AAS, TPR, TPH, TGA, BET, XPS, and Raman techniques. The catalyst is evaluated on time stream and identify its anti-agglomeration property and coking mechanism. From the characterization of TEM and XPS establish the information of Ni particles mobility in the catalyst, which active metal particle size was controlled under the yolk–shell structure framework. Furthermore, the results from TGA, TPH, and Raman analysis of the used Ni@yolk–ZrO₂ catalyst showed the characteristic of inhibiting formation of highly ordered carbon structure

Preparation, modification, and characterisation of Yolk-shell structure based catalysts for synthetic gas production

Hydrogen is an emerging energy carrier for oil refining and fuel cell applications. The development of an efficient and stable catalyst to produce hydrogen gas is required for industrial applications. However critical issues in the catalyst that lead to the deactivation of reactions include active metal particle growth and carbon fouling. Industrial catalysts that are frequently overwhelmed by such issues are substituted or re-treated, which is not time and cost efficient. Therefore, developing durable catalysts that are resistant to sintering and carbon fouling remains an area of interest. A novel and anti-agglomeration Ni@yolk-ZrO2 catalyst is first reported in this thesis. A specific study of the ZrO2 hollow shell showed that the varied porosity of the hollow shell contributed to the catalyst’s ability to inhibit the agglomeration of active Ni particles. The steam reforming of methane was selected as the probe study for this catalyst in this research. Before a thorough analysis of the Ni@yolk-ZrO2 catalyst was performed, the systematic synthesis of Ni@SiO2 was studied. The analysis showed that the Ni particle size can be controlled by tuning the synthesis temperature. Water-to-surfactant ratio in the microemulsion was shown to influence the morphology of the Ni@SiO2 particle. The tetraethyl orthosilicate (TEOS) amount added with fractionated dispensing and the amount of NiCl2 were found to have affected the size and morphology of the Ni@SiO2. For the Ni@yolk-ZrO2 sample, the catalyst was characterised by Transmission Electron Microscopy (TEM) and X-Ray Diffraction. TEM was used for morphology analysis, while X-ray Diffraction was performed for phase analysis and crystallite size measurements. Nitrogen adsorption-desorption isotherm was done to measure specific surface area, total pore volume, and the t-plot micropore volume of the samples. Reducibility analysis of the Nickel species of the Ni@yolk-ZrO2 catalyst was carried out using Temperature Programmed Reduction. The anti-agglomeration property of the Ni@yolk-ZrO2 was established from the TEM and X-ray Photoelectron Spectroscopy analysis. Results showed that the active Ni particles were inside the yolk-shell structured framework, which deterred Ni particles from moving onto the surface of the catalyst. Ni particles were found to be stabilised by the abundant volume of pores in the ZrO2 hollow shell. This result indicates that the Ni particles were anchored by the pores and remained stable during the steam reforming of methane. The Ni@yolk-ZrO2 catalyst was tested by varying the volumes of feed (GHSV) and the steam-to-carbon ratio. This catalyst was also subjected to a recyclability test and proved to be better than conventional impregnated Ni/ZrO2 catalysts. The Temperature Programmed Hydrogenation analysis also proofed that the yolk-shell structure framework inhibited higher order of carbon deposits on the Ni@yolk-ZrO2 catalyst. Varying the porosity of the ZrO2 hollow shell was found to affect the performance of the steam reforming of methane. This varied porosity can be achieved by varying the amount of surfactant during the synthesis of Ni@SiO2@ZrO2. X-ray Photoelectron Spectroscopy analysis results showed that the porosity of the ZrO2 hollow shell contributed to the moderately strong hydrothermal stability of the catalyst for the steam reforming of methane. The hollow shell of the ZrO2 was influenced by the instability of the SiO2. TEM analysis of used BrNi-4.8 catalysts showed that the yolk-shell structure framework of the catalyst collapsed. This result suggests that the shell has weak integrity, and proves that the SiO2 was not able to maintain the yolk-shell framework. The results also suggest that the varied porosity of the ZrO2 hollow shell influences the catalysts’ efficiency even though they share the same yolk-shell structure framework. This is likely due to the differences in the pores of each catalyst configuration, which directly affects the Nickel species involved in the catalytic reaction. Finally, it was demonstrated that the Ni@yolk-ZrO2 catalyst exhibits excellent catalytic performance in comparison to conventional catalysts for the steam reforming of methane. Catalytic activity remained stable and achieved a methane conversion of more than 90 % for 150 hours under operating conditions of GHSV of 50400 mL gcat-1h-1 and S/C = 2.5 at 750 oC

Porosity effect on ZrO2 hollow shells and hydrothermal stability for catalytic steam reforming of methane

Hydrogen is an emerging energy source/carrier for oil refining and fuel cell applications. The development of an efficient and stable catalyst to produce hydrogen-rich gas is required for industrial application. The Ni@yolk-ZrO2 catalyst could be a potential solution to tackle the challenges in hydrogen production. The catalyst was characterized using a combination of XRD, TEM, AAS, TPR, BET, and XPS. In this study, the amount of micropores in ZrO2 hollow shells was demonstrated to influence the catalytic performance. Ni@yolk-ZrO2 catalysts were evaluated for 48 hours under steam reforming of methane and their porosity effect in ZrO2 hollow shells was identified. From the characterization of BET and catalytic evaluation, the physical information of the ZrO2 hollow shell was established, which affected the catalytic performance in steam reforming of methane. Furthermore, the results from XPS and TEM showed that Ni particles were controlled under a ZrO2 yolk-shell structure framework and showed the characteristic of moderately strong hydrothermal stability after the steam reforming test. The catalysts were studied at a GHSV of 50 400 mL g(cat)(-1) h(-1) and S/C - 2.5 at 750 degrees C and they remained stable with methane conversion more than 90% for 48 hours

Size-controlled synthesis of thermal stable single-cored Ru@H-SiO2 core-shell nanoparticles

Single-cored Ru@H-SiO2 (H: hollow) core-shell nanoparticles (NPs) with around 4.3 nm Ru cores and hollow SiO2 shells were prepared successfully. In this synthetic process, we obtained multi-cored Ru@SiO2 NPs initially, single-cored RuO2@H-SiO2 NPs during treatment, and single-cored Ru@H-SiO2 NPs in the end. The Ru@SiO2 NPs were prepared by water-in-oil microemulsion method, and the size and core number of Ru@SiO2 NPs can be controlled. Single-cored RuO2@H-SiO2 NPs and Ru@H-SiO2 NPs were successively obtained by calcination and reduction. The structure showed promising aggregate-resistant performance and potential application in catalysis. (C) 2016 Published by Elsevier B.V

Effect of Pr addition on the properties of Ni/Al2O3 catalysts with an application in the autothermal reforming of methane

Ni/xPr-Al2O3 (x = 5, 10, 15, 20 wt%) catalysts with an application in autothermal reforming of methane were prepared by sequential impregnation synthesis; its catalytic performance was evaluated and compared with that of Ni/gamma-Al2O3 catalyst; the physicochemical properties of the catalysts were characterized by X-ray diffraction (XRD), Transmission electron microscope (TEM), X-Ray Photoelectron Spectrometer (XPS), Thermo Gravimetric Analyzer (TGA) and H-2-temperature programmed reduction techniques (TPR). The results showed that Pr addition promoted the reduction of nickel particle size on the surface. TPR experiments suggested a heterogeneous distribution of nickel oxide particles over xPr-Al2O3 supports and the promotion of NiO reduction by Pr modification. The CH4 conversion increased with elevating levels of Pr addition from 5% to 10%, then decreased with Pr content from 10% to 20%. For the stability catalytic tests, Ni/xPr-Al2O3 catalysts maintained the high activity after 48 h while Ni/Al2O3 had a significant deactivation. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved

Evaluation of Ni/Y2O3/Al2O3 catalysts for hydrogen production by autothermal reforming of methane

Ni/xY(2)O(3)-Al2O3 (x = 5, 10, 15, 20 wt%) catalysts were prepared by sequential impregnation synthesis. The catalytic performance for the autothermal reforming of methane was evaluated and compared with Ni/gamma-Al2O3 catalyst. The physicochemical properties of catalysts were characterized by X-ray diffraction (XRD), Transmission electron microscope (TEM), X-Ray Photoelectron Spectrometer (XPS), Thermo Gravimetric Analyzer (TGA) and H-2-temperature programmed reduction techniques (TPR). The decrease of nickel particle size and the change of reducibility were found with Y modification. The CH4 conversion increased with elevating levels of Y2O3 from 5% to 10%, then decreased with Y content from 10% to 20%. Ni/xY(2)O(3)-Al2O3 catalysts maintained high activity after 24 h on stream, while Ni/Al2O3 had a significant deactivation. The characterization of spent catalysts indicated that the addition of Y retarded Ni sintering and decreased the amount of coke. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved