| Chemical looping reforming?CLR?is a novel and promising technology to produce hydrogen.The technology has a high demand for the selection of oxygen carrier?OC?.Ni-based oxygen carrier attracts extensive attention according to its high activity and excellent oxidation-reduction performance;however,the problem of carbon deposition and sintering remain to be further improved.The perovskite oxides with general formula of ABO3or A2BO4 have high thermal stability and redox catalytic activity.The interaction between perovskite oxides and metal can improve the metal dispersion.The vacancies in perovskite oxides can facilitate the elimination of surface carbon.In this work,we study the OC of Ni-based perovskite oxides in order to solve the issue of carbon deposition and sintering,and explore the influence of promoter insertion to the catalytic performance.In this work,two oxygen carriers with different promoter insertions were prepared by co-precipitation method.The reaction of chemical looping reforming of ethanol was carried out in a fixed-bed reactor,and the OCs were characterized by means of XRD?TEM?H2-TPR?ICP-OES and TGA.The study indicated:?1?the perovskite OCs with spatial limiting effect exhibited good redox performance.The perovskite structure was decomposed and Ni ion escaped from lattice phase to develop into metallic Ni during fuel feed step,and then Ni metal was oxidized into perovskite lattice during oxidation step.The movement effectively restrained the growth of metallic Ni and resulted in highly activity of OC;?2?with Sr addition,the oxygen vacancies increased and thus oxygen delivery capacity of OCs was improved.The anti-carbon ability of OCs was strengthened;?3?compared with Ce promoter,Sr addition more remarkable shortened the‘dead time'that no hydrogen produced in reduction step.It indicates that superior redox performances were attained and high conversion of ethanol was obtained;?4?the OCs with Sr addition have stronger ability to cut off C-C and C-H bond,and water-gas reaction was promoted.The stability of OCs was strengthened markedly.On the basis of previous research,the optimal load capacity of Sr for hydrogen efficiency was determined in chemical looping reforming through the analysis of ethanol conversion,hydrogen selectivity and gas product distribution.The methods of XRD?TEM?TPR and TGA were carried out to characterize OCs.The study indicated that all OCs have small specific surface area,and the OC exhibited the best catalytic performance when the Sr content is 6%.The Ni ion was reduced smaller particle size and high dispersion on the OC surface with perfect Sr content.At the same time,La1.4Sr0.6NiO4-?OC still has high ethanol conversion?90%?and high H2 selectivity?81%?after during 50 activity tests,and it has the least amount of carbon disposition.It indicated that the OC with Sr content of 6%has the best oxygen transmission ability and the best performance of resistance to carbon deposition.Finally,based on the above research,we introduced another metal active component Co into B-site of perovskite oxide in order to prepare double metal oxygen carrier.We prepared the Nix-Co based double metal OC La1.4Sr0.6Ni1-xCoxO4?x=0,0.4,0.8?by impregnation method in order to compare different catalytic performance and different effect for hydrogen production between single metal active component OC and double metal active component OC.We can draw a conclusion by TPR characterization.The introduction of B-site Co strengthened reduction temperature of nickel ion and improved the reducibility of the active component.The strong interaction between Co and Ni suppressed the sintering of active components.The double metal OC got higher catalytic activity and higher hydrogen production rate compared with single metal OC. |
PDF Full Text Request