Affordable Pd Doped Perovskite Based Catalytic Converter for Abating Automotive Emission

Abstract

Automotive emission is burning issue now a days as it release harmful gases like carbon monoxide (CO), unburned hydrocarbons (HC), nitrogen oxides (NOx) and particulate matters (PM) into the atmosphere from the engine exhaust. These pollutants create adverse effect on human beings, animals, vegetation and environment which introduce stringent regulations in the form of emission norms. For the exhaust after treatment, Pt-Pd-Rh based catalytic converters have been used successfully in petrol engine. As noble metals show limitations of sintering at high temperature, lower stability and high cost, perovskite oxides introduced as an alternative catalytic material which have low cost, higher stability and higher activity. Perovskite catalysts prepared by ceramic and wet chemical methods which produce low specific surface area catalyst, it requires high calcination temperature and causes water and air pollution. To overcome the limitations of catalysts prepared by conventional methods, novel method named reactive grinding using planetary ball mill is used due to its simplicity, no requirement of heat treatment and no waste generation. In the present work, perovksite catalysts LaBO3 (Co, Fe, Mn, Cu, Ni) and LaB1-xPdxO3 (B=Co, Fe, Mn and x=0, 0.1, 0.05, 0.025) were prepared by co-precipitation and reactive grinding methods. Prepared catalysts were characterized by various characterization techniques such as TG-DTA, XRD, BET and particle size analysis. The catalytic activity for CO oxidation for perovskites were carried out in atmospheric gas-solid fixed bed catalytic reactor with simulated gas mixture containing 1% CO, 1% O2 and balance N2. The detailed study by varying parameters like milling time, milling speed, ball to powder weight ratio etc. in planetary ball mill was carried out and from the physicochemical properties of prepared catalysts, parameters were optimized as jar: 700 (clockwise), sun wheel: 400 rpm (anticlockwise), ball to powder weight ratio: 15:1 and milling time 11 h. LaCo0.975Pd0.025O3 perovskite prepared by co-precipitation method exhibited higher catalytic activity for CO oxidation from catalysts prepared by co-precipitation method. 10% Pd doped LaFeO3 (LaFe0.90Pd0.1O3) perovskite catalyst prepared by recative grinding method exhibited higher catalytic activity for CO oxidation at lower temperature. New catalyst with 30% Fe and 5% Pd substitution in LaCoO3 (LaCo0.65Fe0.30Pd0.05O3) was prepared by reactive grinding method and checked its activity. LaCo0.65Fe0.30Pd0.05O3 catalyst also exhibited higher catalytic performance for CO oxidation. Time-on-stream study was also carried out for the LaCo0.65Fe0.30Pd0.05O3 catalyst at WHSV = 45000 h-1, temperature = 250 °C and feed gas = 1% CO, 1% O2 and 98% N2 at atmospheric pressure which exhibited continue 100% CO conversion at 250 °C with no reduction in conversion over the period of 24 hours. So, it was selected for the washcoating on 600 cc ceramic monolith and catalytic converter was fabricated and tested with 800cc petrol engine and results were analyzed by five gas analyzer. The actual testing results were 58.8% CO, 47.3% HC and 47.8% NOx conversion.