Combustion Synthesis Of Catalysts For Selective Catalytic Reduction Of NO_x At Low Temperature

Selective catalytic reduction?SCR?of NO_x with NH₃ is a well-known promising technique for removing NO_x.The industrial catalysts for NH₃-SCR are V₂O₅/TiO₂,which have high activity at 300-400°C.To meet more stringent regulation,SCR system should be able to work at low temperature effectively.For example,when diesel engines work at idle and cold start,or SCR system applies in marine vessel after supercharger and power plants after the electric precipitation and desulfurizer,the temperature of tail-end gases is quite low.Hence,developing low temperature SCR catalysts is becoming one of the most important research directions.Solution combustion synthesis?SCS?and flame synthesis?FS?are effective method for production of nanosize materials,which is beneficial to improving the physical and chemical structure of the catalyst,leading to enhance its low temperature performance.This study intends to focus on catalyst formula and preparation methods and develop SCR catalysts with high activity at low temperature,such as a temperature of 250°C or even below.?1?Base on Cu avtive element,catalysts Ti_0.75Ce_0.15Cu_0.05W_0.05O_2-?prepared with solution combustion synthesis technique showed good low temperature activity.The reaction kinetics were performed on catalyst Ti_0.75Ce_0.15Cu_0.05W_0.05O_2-?.The recation rate constant was determined,and the apparent activation energy was also calculated.The possible SCR mechanism over Ti_0.75Ce_0.15Cu_0.05W_0.05O_2-?was studied by in situ diffuse reflectance infrared Fourier transform spectroscopy?DRIFTS?.And ammonia adsorbed on Lewis acid site was more active.?2?Ti_0.75Ce_0.15Cu_0.05W_0.05O_2-?catalyst was optimized.Effects of synthesis conditions on the structure and the performance of Ti_0.75Ce_0.15Cu_0.05W_0.05O_2-?catalyst were investigated.The catalysts synthesized using glycine obtained more porous structure and smaller particle size,which performed good activity at low range temperature.Catalyst Ti_0.75Ce_0.15Cu_0.05W_0.05O_2-?prepared with a higher F/O exhibited higher low temperature activity.Durability test of SO₂was carried out on the optimized catalyst Ti_0.75Ce_0.15Cu_0.05W_0.05O_2-?,which found that the catalyst had a good performance of resisting to SO₂ when in presence of 50 ppm SO₂.?3?This paper has developed premixed flame synthesis of SCR catalyst technology.Promoting vanadium based catalyst through preparation method,flame synthesis have developed nanosized vanadium catalysts.This study intends to investigate the effects of parameters such as the vanadium loading,the flow rate of carrier gas,roating speed,the distance between the aerodynamic nozzle of the burner and the rotating surface and the precursor concentration on the properties of the products.By chemkin,the rules of particles formation was analyzed.The results showed that the particle sizes increased monotonically with precursor concentration due to the increasing of collision frequency.And high temperature of the flame and the long residence time of the particles in high temperature would also increase the particle sizes.Hence,the Ti_0.9V_0.1O_2-?catalysts synthesized with the following conditions exhibited high SCR activity:300rpm rotating speed,17L/min flow rate of carrier gas Ar,304 ppm precursor concentration and 20 mm the axial distance of stagnation plate.At 200-400?,NO conversion of the catalyst was more than 90%.?4?Catalyst Ti_0.9V_0.1O_2-?prepared by SCS and FS were characterized by transmission electron microscopy?TEM?,BET surface area,X-ray diffraction?XRD?,Raman spectroscopy,X-ray photoelectron spectroscopy?XPS?,Temperature programmed reduction by H₂?H₂-TPR?and Temperature programmed desorption of NH₃?NH₃-TPD?.It was found that Ti_0.9V_0.1O_2-?prepared by FS obtained smaller surface areas,but with abundant V and Br?nsted acidity on the catalyst surface,and formed larger average coordination number of vanadium,leading to better medium low temperature activity.Sample Ti_0.9V_0.1O_2-?prepared with FS exhibits good resistance to SO₂.