Modification And Catalytic Performance Of Ni Based Catalyst Deriving From Hydrotalcite For Ethanol Steam Reforming

In the past decades,the increasingly serious environmental crisis and the growing demand for energy have promoted the development of renewable energy and clean fuel technologies.Hydrogen,as a kind of energy,is considered as one of the main sources of clean fuel in the future.Ethanol steam reforming（ESR）technology,especially using biomass ethanol as raw material,is considered to be one of the most suitable hydrogen production technologies for large-scale promotion.However,the sintering of active components in the catalyst and the occurrence of side reactions all lead to the deactivation of the catalyst due to the formation of coke,which hinder the commercialization of the catalyst.Therefore,the current research focus is to develop a highly active catalyst,sintering resistance and resistance to carbon deposition of catalyst.In this paper,the ESR catalyst was prepared by Ni Al Layered double hydroxides（Ni Al-LDHs）as the precursor.The catalysts were modified from two aspects:doping and structure.It is expected to have better catalytic activity and anti-carbon deposition stability for ESR.The main research contents and conclusions are as follows:（1）A series of Ni_xCu_yAl Layered double hydroxides（Ni_xCu_yAl-LDHs）were prepared by co-precipitation method（x:y=Ni:Cu mole ratio）.NiAl-LDHs was modified by adding Cu,and the effects of Cu doping amount on the surface structure,chemical properties and catalytic performance of the catalyst were studied.The results show that the introduction of Cu increases the activity of water gas shift（WGS）reaction at 350-450℃.In addition,Ni-Cu alloy was formed,and the conversion of ethanol was improved under the synergistic action of Ni-Cu alloy.But an excess of Cu in Ni-Cu alloy surface enrichment,sintering,the activity of Ni sites were masked.For example,the Ni₁Cu₁Al catalyst had been producing C₂product acetaldehyde in the temperature range of 350-600℃.In the series of Ni_xCu_yAl,the hydrogen selectivity of Ni₁Cu₁Al was always the lowest at the same reaction temperature.The stability of Ni₅Cu₁Al catalyst was tested under the conditions of water/alcohol ratio of 3:1 and temperature 500℃.The experimental results showed that the catalyst had no obvious deactivation within 10 h,with the conversion rate of 100%and hydrogen selectivity of about69%.To some extent,the addition of Cu improves the stability of the catalyst.（2）By Mg²⁺replace Ni²⁺+Cu²⁺synthesis of a series of NiCuMgAl Layered double hydroxides,is on the basis of NiCuAl catalyst research,guarantee the M²⁺/M³⁺metal cation under fixed proportion.The specific surface area of the catalyst increased from 78.02m²·g^-1to 145.58m²·g^-1with the addition of Mg.When the catalyst Mg/Ni+Cu feed ratio is 2:1,the ethanol conversion rate was always over 99%at 350-600℃,and there was no obvious deactivation in the stability test within 14h.The introduction of alkaline-earth metal Mg,on the one hand,shielded the acid position of Al₂O₃in the catalyst,which could inhibit the dehydration reaction of ethanol and then reduce the amount of carbon deposition.On the other hand,the dispersion of Ni was increased,and the deactivation caused by sintering of active components was reduced to a certain extent.（3）The LDHs and SiO₂nanocomposites,were prepared by sol-gel coating（L@SiO₂）and in-situ co-precipitation（SiO₂@L）.The aim is to use steric hindrance to inhibit the stacking and collapse of hydrotalcite layer.The results of characterization and catalysis showed that the hydrotalcite layer in SiO₂@L catalyst had grown uniformly in situ on the surface of SiO₂,and the active component was more evenly dispersed due to the thinner layer.After calcination,it still maintained a flower-like hierarchical structure,which was conducive to the exposure of active components.Catalytic results also showed that the catalyst had good stability,under the high alcohol content test its stability within 19h no significant inactivation.