Preparation,Characterization And Application Of Functionalized Porous Solid Acid/Base Catalytic Materials

The traditional homogenous catalysts have high catalytic activity,but it is easy to cause a series of ecological environment pollution.The development of new highlyefficient and environmentally-friendly solid catalytic materials has become the focus of researchers all over the world.Metal-organic frameworks(MOFs)and covalent organic frameworks(COFs)are two emerging types of porous materials due to their high surface area,regular and adjustable channels,easy modification,and good thermal and chemical stability.Therefore,these materials have shown broad application prospects in gas storage&separation,catalysis,energy storage,chemical sensing,and drug release&delivery.Herein,we designed a series of novel functionalized porous solid acid-base catalysts by rational post-chemical modification,and further tested their performances on the catalytic conversion of biomass and environmental pollutant gas.The main contents are as follows:(1)The defect sites in metal-organic frameworks(MOFs)can dramatically alter their physicochemical properties.The identification to the accurately local fine structure of defected MOFs and establishing the structure-activity relationship between defected MOFs and their catalytic reaction performance would provide the reliable guidance for the direct synthesis and designation of highly efficient catalytic materials.However,due to the limitations of traditional characterization methods on acidity characterization,the characterizations to the microlocal structure of defect sites and its Lewis acid properties in defected MOFs are extremely challenging.In this chapter,the structural defects of one classical MOF(UiO-66)at different temperatures are analyzed via a series of characterization methods including XRD,BET,FT-IR,TG,and ssNMR.It found that solid state NMR could clearly characterize the strength and contents of Lewis acids of four different chemical shifts(-34 ppm,-36 ppm,-41 ppm,and-50 ppm)of UiO-66 adsorbed with TMP as the probe molecule after heat treatment.At the same time,the defected structures corresponding to the four Lewis acid sites were determined by comparing to the calculated31P chemical shift of adsorbed TMP on possible defected sites of UiO-66.As the temperature increasing,the 31P chemical shift signal of TMP probe molecule gradually increased,which indicates that the UiO-66 Lewis acid content increased significantly after heating treatment.Current work not only provides a reliable method for the quantitative characterization of the concentration and acid strength of defect sites in MOFs,but also deepens the understanding to the microlocalized fine structure of defect sites and its catalytic reaction mechanism.(2)Conventional solid acids usually show lower catalytic activities than liquid acids due to the limitation of acid strength and diffusion in the reactions,to solve the problems of low content of solid acid and weak acid strength,a series of ionic liquid modified UiO-66 solid superacids have been developed by solvothermal synthesis.These solid acids not only have large specific surface area,and regular and stable structure,but also have high acid content(～3.33 mmol/g)and super acid strength(31PTMPO NMR chemical shift 88 ppm).It is found that due to the unique physicochemical characteristics of UiO-66 solid strong acid,methanol is activated in its micropores,showing excellent catalytic activity,and even far better than the commonly used solid acids(Nafion NR50,Amberlyst-15,and SBA-15-SO3H-0.2)and concentrated sulfuric acid in biodiesel reaction.This study provides a new idea for the preparation of novel microporous solid acids with super-strong acid,high acid concentration,high activity,and high reuse performance.(3)To further expand above-mentioned method to prepare new solid acid.In this Chapter,UiO-67 based material containing 2,2’-bipyridine group(UiO-67-bpy)in its framework was prepared by solvothermal synthesis,and then three UiO-67-RSO3H-xs solid acid materials were successfully prepared by introduced the sulfonic acid group on bipyridine.Like the ionic liquid modified UiO-66,UiO-67-RSO3H-xs also show good performance on the esterification reaction of palmitic acid and methanol,the ester exchange reaction of triglycerin palmitate and methanol,and the esterification reaction of sunflower oil and methanol.Although the modification of the acidic ionic liquid group to the UiO-67-bpy material changed the physicochemical property of UiO-67bpy,UiO-67-RSO3H-xs solid acid still maintains high surface area,large porosity,and good thermal stability,which leads to the better catalytic performance and reutilization than the traditional resin solid acid catalysts(Nafion NR50,Amberlyst-15,and SBA15-SO3H-0.2).This study not only expands the preparation method of new porous solid acids,but also provides some guidances for the modification of other porous solid acid materials.(4)Hydrogen sulfide(H2S)is a highly toxic and corrosive industrial waste gascontaining in the combustion of coal,oil,and natural gas.It’s of great significance to ensure the safety of industrial production process and human health to catalysis and eliminate H2S gas selectively.In this work,a class of micromesoporous covalent triazine framework(CTF-1-xs)solid base materials functionalized with abundant adjustable nitrogen structure was prepared by the ion-thermal synthesis method,and further applied for the capture and removal of toxic H2S.The micromesoporous structure and large surface area favor to the mass transfer of reactants and products in catalytic reaction,CTF-1-xs was found to desulfurate H2S with the 12000 mL·g-1·h-1 conversion rate and 100%sulfur selectivity at 180℃.In addition,its catalytic activity is much better than that of commercial materials(such as Fe2O3 and g-C3N4)when the competitive oxidation of other species(such as CO)in an industrial environment was considered.The study shows that CTF-1-xs materials not only have good H2S selective capture performance but also excellent catalytic activity in the preparation of elemental sulfur by selective oxidation of H2S.Moreover,we provide an efficient non-metallic catalyst for the catalytic conversion of H2S gas to sulfur.