Preparation Of Layered Double Hydroxide-based Catalysts And Their Photodegradation And Catalytic Transfer Hydrogenation Properties

Environmental pollution and energy shortage are two major challenges facing economic and social development.Layered double hydroxide materials have a special host-guest structure,large specific surface area,tunability,and mixed metal oxides derived from layered double hydroxide can achieve highly dispersed doped metals at the atomic level.Layered double hydroxide and its derivatives exhibit excellent catalytic performance in photocatalytic degradation of organic pollutants and catalytic hydrogen transfer of biomass,and have good industrial application potential.In this paper,Mg Al layered double hydroxide-based materials were used as catalysts to study their catalytic performance in photocatalytic degradation of tetracycline hydrochloride in water and catalytic hydrogen transfer of furfural to furfuryl alcohol.The main research contents and conclusions are as follows:Mg_xAl layered double hydroxide catalysts with different Mg/Al molar ratios were synthesized by co-precipitation method.The results show that increasing the Mg/Al molar ratio can increase the specific surface area of the catalyst and reduce the grain size.SEM characterization showed that when the Mg/Al molar ratio increased from 2 to 6,the average thickness of layered double hydroxide nanosheets decreased from 28 nm to 16 nm,and the stacking became more fluffy.In the test of photocatalytic degradation of tetracycline hydrochloride（TC）,we found that the photocatalytic performance of layered double hydroxide can be improved by increasing the Mg/Al molar ratio（≤6）.Among them,the Mg₆Al sample showed the best catalytic activity,and the degradation efficiency of 50 ppm TC was 92.9%within 70 min.This is because thinner nanosheets and more fluffy structure make the sample have a larger specific surface area,which is conducive to light absorption and photogenerated charge transfer.The results of cycle stability showed that the activity of the catalyst did not change after 4 times of continuous use,and it had good stability.MgAlFe layered double hydroxide precursors were synthesized by co-precipitation method using Fe³⁺to replace Al³⁺in Mg Al layered double hydroxide.After heat treatment at400℃,Fe³⁺highly dispersed mixed metal oxide c HT-Mg Al Fe-x（x is Fe/（Al+Fe）molar ratio）was obtained.By changing the content of Fe,the crystal structure and surface properties of the mixed metal oxides and their structure-activity relationship with catalytic performance were studied.Due to the introduction of Fe³⁺with a large ionic radius,the thermal stability of the layered double hydroxide precursors decreased,which made the derived mixed metal oxides more compact,and the specific surface area decreased with the increase of Fe substitution.The results of CO₂/NH₃-TPD characterization showed that with the increase of Fe substitution,the number of surface basic sites increased gradually,while the number of surface acidic sites decreased sharply.The catalytic performance of hydrogen transfer of furfural to furfuryl alcohol with isopropanol as a hydrogen donor was tested.It was found that the sample c HT-Mg Al Fe-0.5 had the best catalytic activity.The conversion of furfural was63.5%and the selectivity of furfuryl alcohol was 85.2%at 130℃for 2 h.It was found that the basic sites played a more important role in the reaction than the acidic sites according to the acid/base poisoning experiments,and the reaction mechanism of catalytic hydrogen transfer of furfural to furfuryl alcohol on Mg Al Fe mixed oxide was proposed.The cycle test shows that the activity of the recovered catalyst can be restored after the organic matter adsorbed on the surface is removed by calcination.