Search

[Display omitted] • A coupled chemical looping conversion of glycerol, CO 2 and H 2 O is achevied. • High-purity H 2 and syngas are one-step produced by GO, GDR and WS using OC. • Co-Fe interaction in OC inhibits the formation of carbon. • FeCoCe OC achieve excellent oxygen storage and redox reactions. • OC with 7:5:10 of Co: Fe: Ce presents high activity and stability. A coupled chemical looping conversion of glycerol and CO 2 with thermochemical water splitting (WS) cycle is substantially researched due to its potential for one-step renewable H 2 and syngas production. The major challenge lies on having good controls of redox reactions of the oxygen carriers (OCs) used and its unusual sensitivity to the changes of the compositions, chemical states and structure, etc. Here, we develop the OCs that consists of Fe 2 O 3 -Co 3 O 4 supported on the mesoporous CeO 2 structure (Fe 2 O 3 -Co 3 O 4 /CeO 2), which simultaneously promote glycerol oxidization (GO), dry reforming of glycerol (GDR), and WS processes. The easy migration and activation of lattice oxygen by Fe 2 O 3 -Co 3 O 4 /CeO 2 greatly improved the GO and GDR to produce syngas at the first step, and the pure H 2 production by the reduced Fe 2 O 3 -Co 3 O 4 /CeO 2 achieved excellent WS and oxygen storage at 750℃. The low-content Fe dopant in the OC presented a beneficial effect on the anti-sintering performance, and increase of Co-doping indicated a high activity to WS as well as enhanced GDR. The Fe 2 O 3 -Co 3 O 4 /CeO 2 with 7:5:10 of Co: Fe: Ce molar ratio presented the highest glycerol and CO 2 conversions and the highest H 2 yield, also illustrated the excellent activity and stability in 40 consecutive redox cycles. [ABSTRACT FROM AUTHOR]

A series of multifunctional catalysts were derived from lamellar montmorillonite (MMT) via ultrasound-assisted cation-exchange method. They were characterized by N 2 adsorption-desorption, X-ray diffraction (XRD), H 2 temperature-programmed reduction (H 2 -TPR), H 2 pulse chemisorption, inductively coupled plasma optical emission spectrometry (ICP-OES), and transmission electron microscopy (TEM). The characterization results show that metal-support interaction (MSI) together with Ni and Ca dispersion interrelates with confinement effect of montmorillonite. The CO 2 absorption capacity of CAT-5 (Ca/MMT molar ratio is 5) was still above 20.0% at the tenth cycle. The steam to glycerol molar ratio (S/G) and reaction temperature were investigated, and an S/G = 3 and a temperature of 600 °C were optimized. The hydrogen purity was significantly enhanced by the equilibrium shift of insitu CO 2 removal at 600 °C. CAT-5 presents the best performance considering the synchronized absorption capacity and catalytic activity. Compared with CAT-M, CAT-5 shows higher stability in the multiple reaction-decarbonation cycles, which is due to the elevated sintering resistance of CaO derived from the confinement effect of lamellar structure. [ABSTRACT FROM AUTHOR]

Hydrogen production from sorption enhanced aqueous phase reforming (APR) of biodiesel byproduct glycerol was studied by Ni-based monometallic and bimetallic catalysts supported on gelatinous MgO supports. Compared with Ni-based monometallic catalyst, the H 2 selectivity and glycerol conversion of the Cu–Ni bimetallic catalyst were found to be increased more than 3% and 30%, respectively. Meanwhile, higher reaction temperature was found to have higher H 2 yield with lower H 2 selectivity. The H 2 yield using the catalyst with gelatinous MgO support was 1.25 times higher than that of calcined support. Through in-situ CO 2 capture, the addition of CaO to the Cu–Ni bimetallic catalyst increased more than 58.3% and 14.4% of the H 2 yield and selectivity, respectively. An analysis about liquid product component indicate that the presence of CaO promote the further cleavage of the C–C bond, which further increased the conversion of glycerol. Furthermore, it was found that the presence of CaO could also improve the stability of the catalyst through the control experiments. [Display omitted] • Sorption enhanced APR to H 2 with in-situ CO 2 capture was studied. • Monometallic and bimetallic supported on MgO were developed. • Cu–Ni supported on gelatinous MgO exhibited good APR performance. • H2 yield by gelatinous MgO support was 1.25 times higher than that of calcined MgO. • Presence of CaO in APR improved conversion, selectivity, and stability. [ABSTRACT FROM AUTHOR]

Hydrogen production from chemical looping steam reforming (CLSR) of glycerol was studied by Ni-based oxygen carrier in a fixed-bed reactor. For the fixed-bed reactor configuration, solid Ni-based oxygen carrier is stationary and alternatively exposed to reducing and oxidizing conditions by periodically switching the feed gases. The Ni-based oxygen carrier was prepared by a liquid-state co-precipitation method with rising pH technique and the characterization was performed by X-ray powder diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and N 2 adsorption–desorption. Gaseous products and temperature variety during CLSR process by Ni-based oxygen carrier in a fixed-bed reactor were measured, and the thermodynamic equilibrium calculation was also carried out. The results showed that the Ni-based oxygen carrier synthesized has a dual function and can efficiently convert glycerol and steam to H 2 by redox reactions. The coexisting reactions of glycerol oxidization (or NiO reduction) and steam reforming occurred before the steady stage of hydrogen production in the fuel feed step, and the conversion of NiO to Ni was obtained. Alternating reduction and oxidation reactions enabled Ni-based oxygen carrier to produce H 2 with a concentration of 85% of the equilibrium value at 600 °C, and glycerol conversion was up to 99%. The increase of temperature related to the exothermic reactions by Ni-based oxygen carrier in CLSR process was observed in redox cycles. [ABSTRACT FROM AUTHOR]

In this study, renewable hydrogen production was achieved by coupling of water splitting and glycerol oxidation reforming by chemical looping technology (CLWS-GOR) using the novel Ce–Ni modified Fe-based oxygen carriers (OCs). The OCs were developed by combining metal chelating sol-gel and isometric impregnation method, which exhibited anti-sintering characteristic and lattice oxygen migration ability in CLWS-GOR. The amount of hydrogen between 12.49 and 12.96 mmol in the steam stage was produced from all the OCs with different ratios of Fe, Ce and Ni. However, with the increase of Ce and Ni doping, the production of H 2 and CO in the fuel stage increased, as well as the probability of carbon deposits released in the subsequent steam stage. The H 2 /CO ratio in syngas were easily adjusted by steam to carbon molar ratio (S/C) in chemical looping steam reforming (CLSR), but the effects of steam introducing led to gradual deterioration of OCs. The results proved the OCs prepared by the combination method has high activity and stability for renewable hydrogen production from coupling of CLWS-GOR. [Display omitted] • Coupling of water splitting and glycerol oxidation reforming by chemical looping. • Ce–Ni modified Fe-based OCs were synthesized by combined method. • Pure H 2 was achieved from CLWS-GOR by reduced OCs. • WGS enhancement and the H 2 /CO ratio adjustment were achieved. [ABSTRACT FROM AUTHOR]

Abstract: About 10wt.% of glycerol can be produced during the conversion of vegetable oils or animal fats into biodiesel fuel by the transesterification process. To make use of glycerol and increase its values, H2 production from catalytic steam reforming of glycerol by Ni–Mg–Al based catalysts was evaluated experimentally in a fixed-bed reactor under atmospheric pressure within a temperature range of 450–650°C. The thermodynamic analysis was conducted by using a non-stoichiometric methodology based on the minimization of Gibbs free energy. The Ni–Mg–Al based catalysts were synthesized by the co-precipitation method with rising pH technique. The synthesized catalysts were characterized by the elemental analysis, BET, XRD and SEM methods. All the metals in the catalyst remained in oxide forms and the catalysts had the specific surface areas from 98.542 to 126.777m2/g for different compositions. The results showed that glycerol conversion and H2 selectivity were increased with increasing temperatures from 450 to 650°C. The formations of CH4 and CO in the glycerol steam reforming were almost negligible. Carbon formation in glycerol steam reforming was serious in low temperatures. The catalyst containing NiO of 24.1wt.%, MgO of 26.1wt.% and Al2O3 of 49.8wt.% performed appreciable catalytic activity, and the H2 selectivity was found to be 78.5% and conversion of glycerol was up to 88.0% at 650°C. The effects of the operating conditions including temperature, the ratio of steam to carbon (S/C), glycerol inlet concentration and flow rate of carrier gas on glycerol steam reforming by the optimized catalyst were tested. Based on a kinetic model assuming the power law with a first reaction order, the activation energy and the frequency factor for glycerol steam reforming by the Ni–Mg–Al based catalysts were calculated. [Copyright &y& Elsevier]

[Display omitted] • Hydrogen was efficiently produced from CLSR of biodiesel byproduct glycerol. • Well-order mesoporous CeNiO/MCM-41 and CeNiO/SBA-15 were synthesized for CLSR. • High feeding conversion and H 2 selectivity was achieved by mesoporous OCs. • High loading NiO and CeO 2 on mesoporous OCs achieved excellent CLSR redox cycles. The selection of metal oxides and supports to improve catalytic activity and stability of oxygen carriers (OCs) is crucial for chemical looping steam reforming (CLSR) to hydrogen production. In this study, the Ni-based MCM-41 and SBA-15 OCs with and without CeO 2 promoter were prepared by direct synthesis and impregnation methods. The BET, XRD, TEM, ICP-AES, H 2 -TPR and DSC-TGA were used to analyze the synthesized OCs. Hydrogen production by CLSR using biodiesel byproduct glycerol was studied in a fixed-bed reactor with fuel and air stages. The DSC-TGA experiments were carried out to determine the thermal decomposition of biodiesel byproduct glycerol and the results indicated the exothermic and/or endothermic reactions as a result of secondary reactions and, the main degradation with the mass loss of 85.5 wt% occurred in the stages of 150–500 °C. The mesoporous OCs presented high specific surface area, large pore volume, and uniform pore size. It was found that the NiO and CeO 2 in the mesoporous OCs were first reduced by fuels and the reduced OCs was responsible of steam reforming and water gas shift (WGS) to hydrogen production, and hydrogen selectivity was up to 90% using CeNiO/SBA-15. The mesoporous OCs with Ce promoter greatly shortened 'dead time' (the reduce time of OCs), and effectively suppressed carbon deposited on OCs. High loading of NiO and CeO 2 on SBA-15 improved oxygen transfer and achieved excellent cyclic stability. These findings provide the fundamental understanding and principle of design on the conventional Ni-based OCs with room for further developments in chemical looping process. [ABSTRACT FROM AUTHOR]