Effect of calcination atmosphere on surface defect of nano Zro[subscript 2] and its application as catalysts for biodiesel synthesis

Abstract

In this present research, the nanocrystalline ZrO[subscript 2] supports were prepared using the solvothermal method. The obtained ZrO[subscript 2] powders were treated at 500°C in various atmospheres (Air, H[subscript 2] , N[subscript 2] and O[subscript 2]). Then, the ZrO[subscript 2] supports were impregnated. with tungsten (Vl) chloride which were calcined further to form the oxide phase. Effect of calcinations atmospheres on the physiochemical properties of W/ZrO[subscript 2] catalysts and ZrO[subscript 2] supports were investigated using XRD, BET, Raman spectroscopy, ESR, titration and TEM techniques. BET surface area, crystallite sizes and monoclinic contests of all treated-ZrO[subscript 2] supports were slightly different and ranged between 76 to 95 m[superscript 2]/g, 3.5-6.9 nm and 21-29 wt.%, respectively. The ESR results revealed that the F-center defects on ZrO[subscript 2] supports increased as the calcinations atmospheres became more reducible. Catalytic performances of the W catalysts supported on these treated catalysts were studied in the liquid phase transesterification reaction of triacetin and methnol. The catalytic activities were improved in the order: WZ cal. H[subscript 2] (53%) > WZ cal. N[subscript 2] (40%) > WZ cal. O[subscript 2] (17%) = WZ cal. Air (16%). This result was in good agreement with the increased order of acidity determined by titration and Zr[superscript 3+] determined by ESR. Increasing of acidity was probably due to the increase of dispersion of WO[subscript x] species ZrO[subscript 2] supports.