Abstract
POSS (polyhedral oligomeric silsesquioxanes) nanotechnology was applied for preparation of efficient Ni catalysts for hydrogen production through autothermal reforming of methane (ATR of CH4). The novel metal-POSS precursor [Nickel (II) ‒ HeptaisobutylPOSS (C4H9)7Si7O9(OH)O2Ni] of Ni nanoparticles was introduced into Ce0.5Zr0.5O2 support with following calcination and reduction stages of activation. The peculiarity of the genesis of Ni/SiO2/Ce0.5Zr0.5O2nanomaterials and their characteristics versus deposition mode were studied by X-ray fluorescence spectroscopy, thermal analysis, N2adsorption, X-ray diffraction, high-resolution transmission electron microscopy and H2 temperature-programmed reduction. The two kinds of supported Ni-containing particles were observed: highly dispersed Ni forms (1‒2 nm) and large Ni-containing particles (up to 50‒100 nm in size). It was demonstrated that the textural, structural, red-ox and, consequently, catalytic properties of ex-Ni-POSS catalysts depend on the deposition mode. The increase of a portion of difficultly reduced Ni2+species is found upon application of intermediate calcination during Ni-POSS deposition that has detrimental effect on the activity of catalyst in ATR of CH4. The Ni/SiO2/Ce0.5Zr0.5O2 catalyst prepared by one-step Ni-POSS deposition exhibits the highest H2 yield ‒ 80% at T = 800 °C.
Highlights
Development of efficient and low cost hydrogen production technologies is an urgent task due to the increased demand of clean energy generation [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]
Yields of H2 and CO were determined as percent of the amounts of products produced by the reaction from maximally possible amounts, using the following equations: YH2 = 100%∙VH2out/(2VCH4in + VH2Oin), where YH2 is a yield of H2, %; VH2out is a molar rate of H2 at the reactor outlet, mol/min; VCH4in is a molar rate of CH4 introduced into the reactor, mol/min; VH2Oin is a molar rate of H2O fed into the reactor, mol/min; and YCO = 100%∙VCOout/VCH4in, where YCO is a yield of CO, % VCOout is a molar rate of CO at the reactor outlet, mol/min; VCH4in is a molar rate of CH4 introduced into the reactor, mol/min
It can be noted that according to actual chemical composition of samples, the Si/Ni atomic ratio in the Ni/SiO2/ Ce0.5Zr0.5O2 catalysts differ from Si/Ni atomic ratio in Ni-POSS
Summary
Development of efficient and low cost hydrogen production technologies is an urgent task due to the increased demand of clean energy generation [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]. The stabilization of small Ni nanoparticles in the support matrix is one of the approaches to overcome these obstacles To achieve this effect, the modification of support [28, 29], the improving of preparation method [30], the selection of appropriate metal precursor [31,32,33,34] and the optimization of catalyst activation conditions [35,36,37,38] are widely employed. The average Ni particle size is equal to 4.5 and 8.1 nm for the ex-HDP and ex-PVI catalysts, respectively In this case, the reaction rate of catalysts in SMR increases linearly with the Ni dispersion, while the content of carbonaceous deposits decreases. The results were analyzed in comparison with those for Ni/SiO2 and Ni/Ce0.5Zr0.5O2 catalysts prepared by conventional method
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