Research Of The Novel Metal-organic Frameworks Immobilied Phosphotungstic Acid Preparation And Its Catalytic Properties

Porous metal-organic frameworks are coordination polymers formed by meansof connection metal ions with multifunctional organic ligands, which have nano-sizedspace and potential value on gas storage, adsorption and separation, molecularcatalysis, magnetic materials and other areas. Compared with traditional inorganiczeolites and porous carbon materials, porous metal-organic frameworks could beprepared under mild conditions, be easy to be modified, and have a wealth ofstructural diversity and spatial configuration. This paper aims to study the value ofmetal-organic frameworks as catalyst carriers. In this paper, the different kinds ofmetal-organic frameworks encapsulated phosphotungstic acid (HPWs) catalysts weresynthesized by one-pot synthesis method and mixing stirring synthesis method,respectively. The catalytic performance of the as-prepared composite was investigatedfor the preparation of glutaraldehyde(GA) from the selective oxidation ofcyclopentene (CPE)． Moreover, the catalysts were characterized by differenttechniques to further explore the relation between the catalytic performance and thephysico-chemical structure of the catalysts. The main work of the paper is as follows:1. The novel heterogeneous HPWs@MIL-101catalyst was prepared byimmobilization of tungstophosphoric acids (HPWs) on chromium (III) terephthalatemetal organic framework MIL-101via one-pot synthesis method, and wassystemically characterized by means of XRD, N2adsorption, SEM and FT-IRtechniques. The catalytic performance of the catalysts was investigated for thepreparation of glutaraldehyde (GA) from the selective oxidation of cyclopentene(CPE), using hydrogen peroxide as the oxidant and tert-butanol (TBA) as the solvent.The results showed that12.5%(w) catalyst exhibited100.0%of CPE conversion and72.3%of GA selectivity at the conditions of n(CPE): n(H2O2): n(HPWs)=1000:2500:0.9, V(TBA): V(CPE)=10, reaction temperature=35℃and reaction time=24h. The characterization results illustrated MIL-101has a high specific surface area,stable skeleton structures, and high load capacity of HWPs. Heterogeneous and reusable experimental results showed that the catalyst was a true heterogeneouscatalyst and has a good stability.2. The HPWs@Meso-HKUST-1catalyst was prepared by one-pot synthesismethod using cetyl trimethyl ammonium bromide (CTAB) as a supramoleculartemplate. Their catalytic performances were tested by the selective oxidation ofcyclopentene to glutaraldehyde, using tert-butyl hydrogen peroxide (TBHP) as theoxidant. The results show the catalytic performance of30%(w)HPWs@Meso-HKUST-1is the best. The conversion of CPE and the yield of GA reach93.5%and81.0%, respectively, at the conditions of acetonitrile (ACN) as the solvent andV(ACN):V(CPE)=10, V(TBHP):V(CPE)=8, n(CPE):n(HPWs)=1000:3, reactiontemperature=30℃and reaction time=36h. XRD patterns and FT-IR spectra provethat metal organic framework Meso-HKUST-1exhibite high loading threshold ofHPWs and its crystal structure is perfectly kept after HPWs loading. Moreover, theactive HPWs are dispersedly encapsulated into the cavities of Meso-HKUST-1. TEMphotos and N2adsorption curves showe that the synthesized catalysts have amesoporous structure. Heterogeneous and reusable experimental results show that thecatalyst is a true heterogeneous catalyst and has a good stability.3. The HPWs@UiO-66catalyst was prepared by one-pot synthesis method andits catalytic performances were examined by the selective oxidation of cyclopenteneto glutaraldehyde using hydrogen peroxide as the oxidant and tert-butanol as thesolvent. The results show that that35%(w) catalyst exhibited94.8%of CPEconversion and78.3%%of GA selectivity at the conditions of n(CPE): n(H2O2):n(HPWs)=1000:2500:3.5, V(TBA): V(CPE)=10, reaction temperature=35℃and reaction time=24h. XRD patterns and FT-IR spectra shows that the activeHPWs are highly dispersed into the lattice of UiO-66and the HPWs@UiO-66catalystexhibites a high stability；TG analysis shows there is strong interaction betweenHPWs and UiO-66supports, which increased the thermal stability of HPWs@UiO-66catalyst and effectively prevented the HPWs leaching. Heterogeneous and reusableexperimental results show that the catalyst is a true heterogeneous catalyst and has a good stability.4. HPWs@MOF-5, HPWs@Ni3(BTC)2and HPWs@Zn3(BTC)2catalysts wereprepared by mixing stirring synthesis method. Their catalytic performances wereinvestigated by the selective oxidation of cyclopentene to glutaraldehyde usinghydrogen peroxide as the oxidant and tert-butanol as the solvent and furthermore, theoptimal reaction conditions were found for those catalysts. For the HPWs@MOF-5catalyst: the best reaction conditions are n(CPE):n(H2O2)=1:2.5,HPWs/CPE=0.2(mol.%), reaction temperature=40℃and reaction time=48h.Thecyclopentene conversion and yield of glutaraldehyde can reach100%and82.7%,respectively at the above conditions. For the HPWs@Ni3(BTC)2catalyst: the bestreaction conditions are n(CPE):n(H2O2)=1:2.5, HPWs/CPE=0.3(mol.%), reactiontemperature=40℃and reaction time=36h. The cyclopentene conversion and yieldof glutaraldehyde can reach100%and76.3%, respectively at the above conditions.For the HPWs@Zn3(BTC)2catalyst: the best reaction conditions are n(CPE):n(H2O2)=1:2.5, HPWs/CPE=0.3(mol.%), reaction temperature=40℃and reaction time=48h. The cyclopentene conversion and yield of glutaraldehyde can reach100%and81.9%, respectively at the above conditions. All those experimental results show thatthe hydrothermal and chemical stability of catalysts prepared by mixing stirringsynthesis method are poor. The skeleton structure is unstable and prone to collapse,resulting in active species leaching.