Search

The production of hydrogen-enriched syngas from the thermo-chemical conversion of biomass was studied using Ni/CaAlO x catalysts prepared by co-precipitation method. The effect of Ca addition with different molar ratios of Ca:Al (1:3, 1:2, 1:1, 2:1, 3:1) on the properties and catalytic behavior in relation to syngas production and the coke formation on the surface of the catalysts were investigated. Catalysts were characterized by BET, XRD, TPR, SEM, and TEM. The SEM and TEM results showed that rod-shaped nano-particles were highly dispersed on the surface of the catalyst. The particle size of NiO was slightly affected with the increase of Ca content in the catalyst. It appeared that the selectivity of CO was increased and the selectivity of CO 2 was reduced with the increase of Ca addition to the catalyst. For example, CO 2 concentration was reduced from 20 to 12 vol.%, when the molar ratio of Ca/Al was increased from 1:3 to 3:1 for the Ni/CaAlO x catalyst; it is suggested that the water gas shift reaction was inhibited and CO 2 reforming reactions were promoted in the presence of the catalyst with higher Ca content. The CO/H 2 molar ratio could be manipulated by changing the Ca content in the catalyst, while the H 2 concentration remained almost constant (around 45 vol.%). Thus, using the Ni/CaAlO x catalyst developed in this work could provide a promising route to control the syngas composition, which is an important factor for syngas applications. [ABSTRACT FROM AUTHOR]

Abstract: A series of Ni/SiO2 catalysts have been prepared and investigated for their suitability for hydrogen production and tar reduction in a two-stage pyrolysis-reforming system, using refuse derived fuel (RDF) as the raw material. Experiments were conducted at a pyrolysis temperature of 600°C, and a reforming temperature of 800°C. The product gases were analysed by gas chromatography (GC) and the condensed fraction was collected and quantified using gas chromatography-mass spectrometry (GC–MS). The effects of the catalyst preparation method, nickel content and the addition of metal promoters (Ce, Mg, Al), were investigated. Catalysts were characterised using BET surface area analysis, temperature programmed oxidation (TPO), and scanning electron microscopy (SEM). The TPO and SEM analysis of the reacted catalysts showed that amorphous type carbons tended to be deposited over the Ni/SiO2 catalysts prepared by impregnation, while filamentous type carbons were favoured with the sol-gel prepared catalysts. The influence of catalyst promoters (Ce, Mg, Al) added to the Ni/SiO2 catalyst prepared by the sol-gel method was found not to be significant, as the H2 production was not increased and the tar formation was not reduced with the metal-added catalyst. The highest H2 concentration of 57.9vol.% and lower tar amount produced of 0.24mgtar/gRDF; were obtained using the 20wt.% Ni/SiO2 catalyst prepared by sol-gel. On the other hand a low catalytic activity for H2 production and higher tar produced were found for the impregnated series of catalysts, which might be due to the smaller surface area, pore size and due to the formation of amorphous carbons on the catalyst surface. Alkenes and alcohol functional groups were mainly found in the analysed tar samples, with major concentrations of styrene, phenol, indene, cresols, naphthalene, fluorene, and phenanthrene. [Copyright &y& Elsevier]

Abstract: The steam pyrolysis-gasification of biomass, wood sawdust, was carried out with a Ni/MCM-41 catalyst for hydrogen production in a two-stage fixed bed reaction system. The wood sawdust was pyrolysed in the first reactor and the derived products were gasified in the second reactor. The synthesised MCM-41 mesoporous catalyst supports were impregnated with different Ni loadings (5, 10, 20 and 40wt.%), which were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), temperature programmed reduction (TPR), transmission electron microscopy (TEM) and temperature-programmed oxidation (TPO). NiO particles were homogeneously dispersed inside the pores of 5, 10, and 20wt.% Ni/MCM-41 catalysts; however, more bulkly NiO particles (up to 200nm particle size) were detected outside the pores with an increase of the Ni loading up to 40wt.%. Gas production was increased from 40.7 to 62.8wt.%, hydrogen production was increased from 30.1 to 50.6vol.% of total gas composition when the Ni loading was increased from 5 to 40wt.% during the pyrolysis-gasification of wood sawdust. This work showed low coke deposition (from 0.5 to 4.0wt.%) with valuable bio-oil by-products using the Ni/MCM-41 catalyst. The highly efficient conversion of renewable biomass resource to hydrogen and bio-oil with very low coke deposition indicates that biomass gasification on Ni/MCM-41 catalysts via two-stage reaction is a promising method for the development of the biorefinery concept. [Copyright &y& Elsevier]

Abstract: Steam reforming of ethanol to produce hydrogen was carried out using a two-stage reaction system with several nano-Ni/SiO2 catalysts prepared at different citric acid (CA) contents using the sol–gel process. The fresh (non-calcined and calcined) catalysts and the reacted catalysts were analysed using surface area and pore size analysis, Fourier-transform infrared (FTIR) spectroscopy, thermo-gravimetry analysis (TGA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that a meso-structured material was produced at Ni:CA ratios lower than 1:0.5; and the pore volume of the catalyst was increased when more citric acid was used during the sol–gel preparation. Gas and hydrogen yield were observed to be increased when the Ni:CA ratio was reduced from 1:0.5 to 1:3.0; however, gas concentration was slightly changed for the catalysts prepared at different Ni:CA ratios. In addition, coke formation was increased from 0.7 to 7.5wt.% when the Ni:CA ratio decreased from 1:0.5 to 1:3.0. It was also found that the Ni/SiO2 catalyst prepared at the low CA content (Ni:CA=0.5) was non-stable during the ethanol steam reforming process; since sintering was obtained as observed using TEM analysis of the used catalyst. [ABSTRACT FROM AUTHOR]

A coaxial dielectric barrier discharge (DBD) reactor has been developed for plasma-catalytic conversion of pure CO 2 into CO and O 2 at low temperatures (<150 °C) and atmospheric pressure. The effect of specific energy density (SED) on the performance of the plasma process has been investigated. In the absence of a catalyst in the plasma, the maximum conversion of CO 2 reaches 21.7% at a SED of 80 kJ/L. The combination of plasma with BaTiO 3 and TiO 2 photocatalysts in the CO 2 DBD slightly increases the gas temperature of the plasma by 6–11 °C compared to the CO 2 discharge in the absence of a catalyst at a SED of 28 kJ/L. The synergistic effect from the combination of plasma with photocatalysts (BaTiO 3 and TiO 2 ) at low temperatures contributes to a significant enhancement of both CO 2 conversion and energy efficiency by up to 250%. The UV intensity generated by the CO 2 discharge is significantly lower than that emitted from UV lamps that are used to activate photocatalysts in conventional photocatalytic reactions, which suggests that the UV emissions generated by the CO 2 DBD only play a very minor role in the activation of the BaTiO 3 and TiO 2 catalysts in the plasma-photocatalytic conversion of CO 2 . The synergy of plasma-catalysis for CO 2 conversion can be mainly attributed to the physical effect induced by the presence of catalyst pellets in the discharge and the dominant photocatalytic surface reaction driven by the plasma. [ABSTRACT FROM AUTHOR]

The emerging integrated CO 2 capture and utilization (ICCU) potentially contributes to net zero emissions with low cost and high efficiency. The catalytic performance in ICCU process is highly restricted by the equilibriums of carbonate decomposition and dry reforming of methane (DRM). Here, we engineer a unique yolk-shell dual functional nanoreactor construction to improve the catalytic performance via confined catalysis. By tailoring the carbonates decomposition kinetics and confining the CO 2 diffusion path, ∼92% CO 2 conversion is achieved over (Ni/Ca)@Si and shows no distinct activity loss in 10 cycles at 650 °C. The formed Ca 2 SiO 4 shells restrain the sintering of CaO yolks by acting as physical barriers, and stabilize the Ni particle size. It is also confirmed on in situ DRIFTS that the integrated DRM might occur via carbonyls, formates and CHO intermediates, in which formates species are highly dependent on Ni-carbonates interfaces. [Display omitted] • Ni-functionalized Ca@Si yolk-shell nanoreactors achieves effective CO 2 capture and in situ methane dry reforming. • Yolk-shell structure promote the catalytic performance by confined catalysis. • Ca 2 SiO 4 shell stabilizes both the CaO yolk and catalytic sites. • Formates are dependent on Ni-carbonates interfaces. [ABSTRACT FROM AUTHOR]