Synthesis, characterization and evaluation of niobium catalysts in the flash pyrolysis of glycerol

Abstract

Niobium catalysts supported on sodium vermiculite (Nb2O5/V0) and vermiculite treated with hydrochloric acid (Nb2O5/V3) were prepared by the incipient impregnation method. The unsupported catalyst, niobium pentoxide, was also synthesized. The catalysts were characterized by X-ray diffraction, adsorption-desorption of nitrogen, scanning electron microscopy coupled with energy dispersive spectroscopy, UV–vis diffuse reflectance spectroscopy and Raman spectroscopy. The characterization techniques used in the analysis of the physico-chemical properties of the catalysts showed the presence of Nb2O5 on sodium vermiculite (V0) and activated vermiculite (V3) in different phases. The best dispersion of niobium oxide, as expected, was on the V3 support (SBET = 464.5 m2 g−1), due to its greater specific area compared to V0 (SBET = 0.7 m2 g−1). The rapid pyrolysis of the glycerol in the presence of catalysts Nb2O5/V0, Nb2O5/V3 and Nb2O5 was investigated using Py-GC–MS. The results showed high decomposition of glycerol with Nb2O5 (82.2%), with higher yields of oxygenated products such as organics acids (25.1%), alcohols (19.8%) and esters (23.7%). In comparison, in the presence of Nb2O5/V3 decarboxylation was greater (CO2 = 6.4%), no esters were identified, and production of organics acids (15.9%), alcohols (19.7%) and aldehyde (10.8%) were favored. Nb2O5/V0 formed products similar to pyrolysis, probably because the catalyst has low acidity and small specific area. Thus, the results of glycerol pyrolysis application showed better performance of Nb2O5 and Nb2O5/V3, due to the efficiency in obtaining oxygenated products with industrial applicability through glycerol.