Silica nanostructures, with variable diameter and mesopore size distribution, modified with tungstophosphoric acid as catalyst in the synthesis of quinoxalines

A. SOSA; L. PIZZIO; G. ROMANELLI

Revista Colombiana de Química

UNC

Año: 2020

0120-2804

Tungstophosphoric acid supported on silicananostructures (SNX#WPA) with variablediameter and mesopore size distributionwere synthetized. Silica nanostructures(SNX) were prepared in octane/aqueousmedia using polystyrene and CTAB as organictemplates. The materials were characterizedby XRD, SEM, TEM and dinitrogen adsorption/desorption isotherm analysis. The octane/water ratio influenced the morphology andsize of SNX prepared, as well as its pore sizedistribution. The SNX samples obtainedusing OCT/H 2 O ratios in the range 0.07-0.35(SN4, SN5, and SN6 samples). present small(5-6 nm) and large (28-34 nm) mesopores(mainly generated by polystyrene). Largemesopores and their volume contributionwere clearly higher than in the SN1, SN2, andSN3 samples. The structure and morphologyof SNX#WPA samples were similar to those ofthe SNX. Furthermore, the characterization ofall the SNX#WPA materials by FT-IR and 31 PNMR indicated the presence of undegraded[PW12O40] 3− and [H3-XPW12O40] (3-X)−species. According to the potentiometrictitration results, the solids presentedvery strong acid sites. The performanceof SNX#WPA materials as catalysts in thesynthesis of quinoxalines was evaluated. Theyields achieved were high, without formationof by-products resulting from competitivereactions or decomposition products, so theprepared materials are highly selective andreusable catalysts.