Preparation Of Ni-La/ZnO Based On ZIF-8 And Its Catalytic Hydrolysis Of Cellulose Into Small Molecule Polyols

With the gradual depletion of reserves of petroleum,natural gas,coal and other fossil resources,the research of renewable resources has attracted more and more attention.Biomass resources has the advantages of renewable,abundant reserves and clean,and it is regarded as an important substitute for fossil energy.Cellulose is one of the most widely distributed and abundant biomass resources in nature,it is one of the most important ways to utilize biomass resources to convert cellulose into diol under the action of catalyst.Therefore,this paper designs and synthesizes a zinc-based catalyst to realize the efficient conversion of cellulose hydrolysate to diols.ZnO,as an amphoteric oxide,can provide acid and base sites at the same time to promote hydrolysis of cellulose and isomerization of sugar;Ni as non-noble metals can provide hydrogenation sites that favor the hydrogenation of cellulose.Ni/ZnO catalysts with different Ni contents were prepared,and the hydrogenolysis experiment of cellulose was carried out.The experimental results showed that 15%Ni/ZnO catalyst had the best catalytic activity,the conversion of cellulose reached 100%,the yield of 1,2-propylene glycol（1,2-PG）reached 12.7%,and the yield of ethylene glycol（EG）reached 8.9%.In order to improve the selectivity of Ni/ZnO catalyst to diols,Ni/ZnO was modified with transition metal and applied to the reaction of cellulose hydrolyzing diols to select the transition metal with the best modification effect.In this experiment,Ni-X/ZnO（X=La,Cr,Y,Ce,W）catalyst was prepared by maceration-calcination-reduction method based on ZIF-8,and it was applied to the reaction of cellulose hydrolyzing diols.The experimental results showed that La³⁺had the most significant effect on improving the catalytic activity of Ni/ZnO.In this paper,the prepared Ni-La/ZnO catalyst was used in the reaction of preparing diols by hydrohydrolysis of cellulose.The catalytic performance of the Ni-La/ZnO catalyst was analyzed by changing the loading capacity and preparation conditions.The experimental results showed that:When the Ni and La load mass fractions were 15 wt%and 40 wt%,the calcination temperature was 500°C,and the calcination time was 4 h,the catalyst had the best catalytic activity,the conversion rate of cellulose to diols was 100%,the yield of 1,2-PG reached the highest 38.6%,the yield of EG reached the highest 25.1%,and the total yield of diols reached 63.7%.Through SEM,TEM,XRD,BET,XPS,TPD and other characterization methods,the morphology and structure of the Ni-La/ZnO catalyst,element valence,particle size and acid-base site properties were studied,and the modification effect of La³⁺was analyzed.The results showed that La³⁺inhibited the crystal growth of ZnO,reduced the particle size,and increased the dispersion of the catalyst.At the same time,La³⁺acted as an electron donor to transfer electrons from lattice oxygen atoms to metal atoms,enhancing the interaction between reactant molecules and the surface of the catalyst,and increasing the alkaline site of the catalyst.The catalytic performance of the prepared Ni-La/ZnO catalyst was studied in the reaction of preparing diols from cellulose hydrolysate.The effect of the experimental conditions of cellulose hydrolysate on the preparation of diols from cellulose by Ni-La/ZnO catalyst was investigated by controlling the single variable method.The results show that when the initial hydrogen pressure of 4 MPa,reaction temperature was 245°C,the reaction time was 3 h,Ni-La/ZnO catalyst hydrogen cellulose solution for glycol had the high yield rate,cellulose conversion rate reached 100%,the total yield reached 63.7%glycol,among them,the yield of1,2-PG is 38.6%,the yield of EG is 25.1%.In addition,cyclic experiments were carried out on Ni-La/ZnO to test the stability of the catalyst.The results showed that the Ni-La/ZnO catalyst had stable chemical properties due to the strong interaction between La and ZnO caused by the transfer of electrons from O_latto Zn²⁺by La³⁺.Based on the above analysis,the main reaction paths for the preparation of diols from cellulose hydrolyzed by Ni-La/ZnO catalyst were proposed:1)cellulose was hydrolyzed to glucose at the acidic site of the catalyst;2)fructose was heterogenously constituted by glucose at the base sites provided by La³⁺and ZnO.3)under the action of La³⁺,glucose and fructose react with RAC to produce glycolaldehyde and acetone alcohols;4)glycolaldehyde and acetone alcohol were hydrogenated on Ni to form EG and 1,2-PG.