Preparation Of Ni-Mo Catalysts And Their Hydrodeoxygenation Properties

Over-exploitation and large-scale consumption of fossil energy have caused serious damage to the global ecosystem.Therefore,the most urgent task at present is to develop and apply large-scale green and environmentally friendly new renewable energy sources on a large scale.Biomass is composed of the main elements of carbon,hydrogen,and oxygen,and it has become a green and environmentally friendly substitute for manufacturing biofuels,fine chemicals,and carbon materials.Lignin can be efficiently converted into a liquid product through liquefaction or cracking,that is,biomass oil,which is mainly composed of phenolic oxygenates,resulting in low combustion calorific value and instability of the oil.The oxygen content of the bio-oil needs to be reduced by catalytic hydrodeoxygenation purification,and its key is the development of highly active bimetal catalysts.According to the current problems of the catalyst and the hydrodeoxygenation?HDO?reaction mechanism,this article mainly develops the following two aspects of work:Firstly,using nickel acetate,ammonium molybdate and urotropine as raw materials,a Ni-Mo-N catalyst was prepared by precipitation reaction and gas phase reduction.A variety of characterization methods were adapted to analyze the phase and morphology structure of the catalyst,and acetophenone was used as the model compound to evaluate the hydrodeoxygenation activity of the catalyst.By studying the influence of different Ni/Mo ratio,N content and reduction temperature on the catalyst activity,it is concluded that Ni₂Mo₃N is the active component of the catalyst.In the hydrodeoxygenation of acetophenone to ethylbenzene,Ni-Mo-N-2-3-700showed the best catalytic performance.Under the conditions of 150°C and hydrogen pressure of 3 MPa,the conversion and deoxygenation rate of acetophenone reached100%after 1 h of reaction,and the selectivity of ethylbenzene was as high as 99.1%.The high activity of the catalyst was related to the synergistic effect of highly dispersed Ni⁰and molybdenum nitride in Ni₂Mo₃N.After 5 consecutive reactions,the catalyst activity decreased slightly,showing good stability.Comparing the characterization results of the catalyst before and after the reaction,no carbon deposits were generated on the surface of the catalyst after the reaction,and its slight deactivation might be caused by the loss of N.Secondly,the Ni-Mo-O precursor was prepared by hydrothermal method,then the Ni-Mo O_3-xcatalyst was prepared by reduction after calcination,and the typical oxygen-containing compounds of lignin?phenols and dimers?were used as simulated substrates to evaluate the HDO reactivity of the catalyst.Characterization results showed that the addition of Ni promoted the reduction of molybdenum oxide to form Mo O_3-x,and there was a strong metal-support interaction?SMSI?between Ni and Mo O_3-x.Catalytic performance test results showed that the Ni-Mo-O catalyst prepared by this method had excellent HDO activity.When the Ni/Mo molar ratio was 2 and the calcination temperature and reduction temperature were 500°C and 300°C,respectively,the prepared catalyst had the best HDO activity:under the conditions of150°C and hydrogen pressure of 4 MPa,after 8 hours of reaction,the conversion rate of p-methylphenol was 100%,and the deoxygenation rate was 99.3%.The high catalytic activity of the catalyst was closely related to metallic Ni,oxygen vacancies,and metal-vacancy interfaces,and the mechanism of hydrodeoxygenation of p-methylphenol on the catalyst was deduced,that is,Ni as a hydrogen overflow site provided dissociated hydrogen,while the oxygen vacancies of Mo O_3-xadsorbed oxygen-containing groups and promoted the cleavage of C-O bonds.Due to the strong hydrogenation activity of Ni,the deoxygenation reaction path of p-methylphenol was mainly hydrogenation-dehydration to generate naphthenes.After three consecutive cycles of reaction,the catalyst activity decreased slightly,but after simple hydrogen reduction treatment,its catalytic performance was completely restored.In addition,the catalyst also showed good deoxygenation activity in the deoxygenation reaction of other lignin bio-oil derivatives,and had good universal applicability.