Jangam Ashok

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.

Ni and/or Ni–Cu alloys supported over SiO2 catalysts synthesized via phyllosilicate structures for steam reforming of biomass tar reaction

In this paper, we describe the synthesis of Ni/SiO2 and Ni–Cu/SiO2 catalysts derived from phyllosilicate structures (Ni/SiO2P and Ni–Cu/SiO2P, respectively) for steam reforming of biomass tar reaction. The steam reforming of biomass tar reaction was investigated with cellulose as a biomass model compound. The influence of steam-to-carbon ratio and reaction temperatures was also explored. Overall, the catalysts synthesized via phyllosilicate structures gave better catalytic performance than the catalysts prepared by the impregnation method. An optimum catalyst composition of 30Ni–5Cu/SiO2P gave superior catalytic performance in terms of stability and activity compared to all other catalysts. At 600 °C, about 78% of biomass was converted to gaseous products over 30Ni–5Cu/SiO2P, which is the highest among all the catalysts tested. Temperature-programmed reduction results indicate that the metal–support interaction of Ni/SiO2P catalyst prepared via phyllosilicate structures is stronger due to the unique layered structure compared to that prepared by conventional impregnation (10Ni/SiO2). The formation of a unique layered structure in Ni/SiO2P and Ni–Cu/SiO2P was also confirmed through TEM analysis. The surface elemental composition results obtained from XPS analysis show that the Cu/Ni surface molar ratio for Ni–Cu/SiO2P catalysts is consistent with the actual molar ratio values obtained from SEM-EDX analysis. This result suggests that the bimetallic catalysts synthesized via the phyllosilicate structure route can yield uniformly distributed alloy species.

Promotion of the Water-Gas-Shift Reaction by Nickel Hydroxyl Species in Partially Reduced Nickel-Containing Phyllosilicate Catalysts

The role of surface hydroxyl species generated by partially reduced Ni‐containing phyllosilicate structures (Ni/SiO2P) in promoting the water‐gas‐shift (WGS) reaction and methane suppression was investigated. To analyze the effect of the surface hydroxyl species, Ni/SiO2P catalysts reduced at various temperatures were employed. All the Ni/SiO2P catalysts showed enhanced catalytic performances and methane suppression compared to the conventional Ni/SiO2 catalyst. As revealed by diffuse‐reflectance infrared Fourier transform spectroscopy (DRIFTS), methane suppression could be attributed to the inhibition of the formation of nickel subcarbonyl species, and the promotion of WGS activity was attributed to the involvement of surface hydroxyl species (Ni−OH, 3626u2005cm−1, and Si−OH, 3740u2005cm−1). The Ni/SiO2P catalyst reduced at 600u2009°C showed exceptionally superior performance to the other catalysts in the water‐gas‐shift reaction in terms of turnover frequency (2.79u2005s−1) and hydrogen formation rates (492.63u2005μmol H2u2009g−1u2009s−1) at 375u2009°C.

Synthesis and evaluation of highly dispersed SBA-15 supported Ni–Fe bimetallic catalysts for steam reforming of biomass derived tar reaction

Highly dispersed Ni–Fe bimetallic catalysts supported on mesoporous SBA-15 were synthesized via an incipient wetness impregnation method by impregnation of a small amount of oleic acid mixed with a metal precursor on the SBA-15 support. This catalyst system was then tested for the steam reforming of biomass tar. Cellulose was used as a biomass model compound for this reaction. Among the various compositions tested, an optimum catalyst composition of 6Ni–1Fe/SBA-15 gave superior catalytic performance in terms of stability and activity. At 600 °C, about 90% of biomass was converted to gaseous products over the 6Ni–1Fe/SBA-15 catalyst, which was the highest among all the catalysts tested. From X-ray diffraction analysis, the Ni metal and Ni–Fe alloy crystallite sizes were barely distinguishable due to the formation of nano-catalysts less than 3 nm in size. Metal particles of less than 3 nm in size were further confirmed through TEM analysis. Moreover, temperature programmed reduction studies indicate a uniform distribution of bi-metallic Ni–Fe species which possess strong metal–support interactions with the mesoporous SBA-15 support. This was also indicated via X-ray photoelectron spectroscopy results. TGA studies over the spent catalysts showed that all Fe containing catalysts generally had lower carbon deposition rates compared to those over the 7Ni/SBA-15 catalyst.

Ni-phyllosilicate structure derived Ni–SiO2–MgO catalysts for bi-reforming applications: acidity, basicity and thermal stability

In this work, Ni–SiO2–MgO materials synthesized via Ni-phyllosilicate (PS) intermediates were explored for bi-reforming of methane (BRM) reaction. The influence of steam and reaction temperature was also investigated for the BRM reaction. Overall, the 15 wt% Ni–30 wt% SiO2–55 wt% MgO (Ni–SiO2–MgO[55]) catalyst maintained exceptional catalytic performance (CH4 and CO2 conversions were 80% and 60%, respectively) at 750 °C for 140 h with negligible carbon deposition and also showed a stable H2/CO of 2.0. The best catalytic performance of the Ni–SiO2–MgO[55] catalyst is attributed to its enhanced basicity strength, reasonable moderate acidity strength and structural stability during high temperature reforming reaction. The formation and presence of Ni–Mg-containing phyllosilicates in fresh and reduced catalysts respectively was confirmed by TEM images and XRD analysis. The Tmax of around 750 °C in TPR profiles of Ni/SiO2–MgO catalysts further confirms the strength of interactions between Ni and SiO2–MgO support species.

Nickel-based Catalysts for High-temperature Water Gas Shift Reaction-Methane Suppression

This article provides a critical review of Ni‐based catalysts employed in high temperature and ultra‐high temperature water gas shift reaction (WGS) for hydrogen production and methane suppression. The promotional role of nature and type of active metal and support for WGS reaction is discussed with respect to activity and selectivity. This review mainly covers the recent strategic catalytic formulations like promotion with alkali metals, alloying with another metal and core@‐shell‐like structures for suppressing methanation during WGS reaction. The change in nature and strength of CO adsorption over modified Ni‐surfaces is discussed using available inu2005situ CO‐DRIFTS results. The various WGS reaction and CO methanation pathways are also presented together with insights gained from computational DFT studies.