Highly Stable Crystalline Catalysts Based on a Microporous Metal−Organic Framework and Polyoxometalates

Abstract

A series of remarkable crystalline compounds [Cu(2)(BTC)(4/3)(H(2)O)(2)](6)[H(n)XM(12)O(40)].(C(4)H(12)N)(2) (X = Si, Ge, P, As; M = W, Mo) were obtained from the simple one-step hydrothermal reaction of copper nitrate, benzentricaboxylate (BTC), and different Keggin polyoxometalates (POMs). In these compounds, the catalytically active Keggin polyanions were alternately arrayed as noncoordinating guests in the cuboctahedral cages of a Cu-BTC-based metal-organic framework (MOF) host matrix. X-ray crystallographic analyses, TG, FT-IR, UV-vis, N(2) adsorption studies, and acid-base titration demonstrated their high stability and toleration for thermal and acid-base conditions. No POM leaching or framework decomposition was observed in our study. The representative acid catalytic performance of a compound containing PW(12) species was assessed through the hydrolysis of esters in excess water, which showed high catalytic activity and can be used repeatedly without activity loss. Moreover, catalytic selectivity, which is dependent on the molecular size of substrates, and substrate accessibility for the pore surface were observed. It is the first time that the well-defined, crystalline, MOF-supported POM compound has behaved as a true heterogeneous acid catalyst. The unique attributes of MOF and well-dispersed level of POMs prohibited the conglomeration and deactivation of POMs, which allowed for the enhancement of their catalytic properties.

Cr-MIL-101 encapsulated Keggin phosphotungstic acid as active nanomaterial for catalysing the alcoholysis of styrene oxide

“…It should be mentioned that MIL-101 with a BET surface area greater than 4500 m 2 /g is very difficult to obtain due to the presence of trapped recrystallised H 2 BDC synthesis residue within the pores of MIL-101. 16 The presence of free dicarboxylic acid impurities in MIL-101 samples was evidenced by IR spectra which showed an absorption band at 1728 cm -1 ( Figure S1, Supporting Information). 11h Although many attempts have been made to increase the purity of MIL-101 through various purification steps, the BET surface area of MIL-101 is limited in the range of 2700-4300 m 2 /g.…”

Inorganic-organic hybrids constructed of bis(undecatungstogermanate)lanthanates polyoxoanions and oxalate-bridged dinuclear copper complexes and their magnetic properties

“…Chinese Sci Bull, 2011Bull, , 56: 2331Bull, −2336Bull, , doi: 10.1007 Recently, the successful design and synthesis of polyoxometalates(POMs)-based hybrids has attracted considerable interest because of their diverse structures and topological properties, as well as their potential applications in catalysis [1][2][3][4]. Polyoxometalates with a strong ability to accept electrons, have been extensively used as inorganic building blocks for the construction of these materials containing organic complexes.…”

Solvent-Free Biginelli Reactions Catalyzed by Hierarchical Zeolite Utilizing a Ball Mill Technique: A Green Sustainable Process

“…To overcome these drawbacks, heterogenization of HPAs into different host supports like silica [29] and activated carbon [30] were reported. Nonetheless, these braced catalytic reagents lean towards controlled POM loading, display some leaching and are liable to accumulation [31]. On the other hand, dihydropyrimidinones were synthesized via Biginelli cyclocondensation utilizing KSF montmorillonite [32] and zeolite [33] catalysts.…”