Loading of MOF-5 and MOF-177 with Cu and ZnO nanoparticles by gas-phase infiltration with organometallic precursors: Properties of Cu/ZnO/MOF as catalysts for methanol synthesis

We have been studying the loading of MOFs with functional metal and metal oxide nanoparticles without destroying the crystalline order of the host lattice aiming at novel metal/support materials for applications in heterogeneous catalysis. The MOFs are suggested to be viewed as solid solvent cages stabilizing the imbedded nanoparticles by comparably weak interfacial interactions. The materials [Zn4O(bdc)3] (MOF-5, bdc = 1,4-benzendicarbocylate) and [Zn4O(btb)2] (MOF-177, btb = benzene-1,3,5-tribenzoate) were loaded with [CpCuL] (L = PMe3, CNtBu) and, in the case of MOF-5, additionally with ZnEt2 leading to the isolable inclusion compounds precursor@MOF-5 and precursor@MOF-177. These intermediates were then converted into Cu/MOF, ZnO/MOF and Cu/ZnO/MOF by various methods which will be presented. The analytical and spectroscopic properties of the loaded MOFs are discussed based on PXRD, HRTEM, EXAFS, UV-VIS, FTIR and MAS NMR data. Catalytic activities for methanol formation from CO/CO2/H2 synthesis gas were found: 10% for Cu/MOF-5 and 60% for Cu/ZnO/MOF-5 as compared with the activity of an industrial reference catalyst Cu/ZnO/Al2O3 (100%). The specific activity based on the rather low Cu loading (1-10 wt.%) were however much higher as compared with the industrial system (Cu, 40-60 wt.%). This observation will be discussed in terms of the strong metal support interaction in heterogeneous catalysis.