Synthesize of magnetite Mg-Fe mixed metal oxide nanocatalyst by urea-nitrate combustion method with optimal fuel ratio for reduction of emissions in diesel engines

Abstract

Abstract In the present study, Mg0.25Fe2.75O4 nanocatalyst for reduction of emissions in diesel engine was fabricated via urea-nitrate combustion method. The effect of urea concentrations as fuel on its structural characteristics and Oxygen Storage Capacity (OSC) was thoroughly investigated. The results of various characterization analyses showed that fuel ratio significantly affects crystallinity, textural, size and morphology of particles, and thermal stability of nanocatalyst. These are mainly due to increase in combustion temperature and duration. The Mg0.25Fe2.75O4 fabricated at fuel ratio of 2.5 times of stoichiometric ratio exhibited the lowest weight loss/high crystallinity (less than 1 wt %) and lowest lattice parameter (8.346 A) which are related to well diffusion of Mg cations into ferric oxide as host. The Raman and FTIR analyses showed the existence of strong peaks correspond to formation of tetrahedral and octahedral sublattices and also the formation of spinel structure of MgFe2O4. The reduction in crystalline size, obtained with higher amount of fuel, resulted in a higher surface area (23.6 m2/g), higher pore volume (0.0950 cc/g) and proper particle size distribution (25–35 nm). These cause a better catalytic activity. Moreover, the enhanced OSC (8661 μmol H2/g) along with shifting the reduction peaks to lower temperatures, as major attributes in relation to catalytic technologies, confirmed the strong effect of fuel ratio of 2.5 on fabrication process of Mg0.25Fe2.75O4. Finally, the highest reduction in HC (33%), CO (14-17%), PM1.0 (16%), and CO2 (12%) achieved, using the optimum sample-mixed diesel fuel at 90 ppm.