Catalytic oxidation of toluene over Co-Cu bimetallic oxides derived from CoyCu3−y-MOF-74

Abstract

As a precursor material, CoyCu3−y-MOF-74 has been synthesized by using a cost-effective and environmentally friendly mechanochemical method. It had a uniform nano-morphology and a controllable stoichiometric composition. By calcinating the CoyCu3−y-MOF-74 material, a bimetallic Co-Cu oxide catalytic material, with the formula M-CoyCu3−yOx, could, thereafter, be prepared. It was later on used for catalytic oxidation of toluene. The effect of calcination temperature and Co/Cu molar ratio on the redox properties, catalytic activity, and structural properties of the catalyst, were also systematically studied. The M-Co2Cu1Ox catalyst showed a complete toluene conversion of 1000 ppm toluene at 225 ℃ and with a under weight hour space velocity of 30,000 ml/ (g h). The corresponding conversion temperature for 50% and 90% of the original amount of M-Co2Cu1Ox (i.e., T50 and T90) were 202 and 220 ℃, respectively. X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and electron paramagnetic resonance (EPR) results also showed a high density of oxygen vacancies in M-Co2Cu1Ox. Also, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments indicated that benzaldehyde and benzoic acid were the main intermediates formed during the catalytic oxidation of toluene. In addition, the M-Co2Cu1Ox catalyst did also show an excellent durability and good water resistance by exposing it to a 5% water vapor for 24 h. Thus, the green and facile mechanical synthesis of the MOF-74 precursor has been proven to be very beneficial for the design and synthesis of a mixed metal oxide catalyst with a high toluene catalytic oxidation efficiency.