Selective Catalytic Reduction Of Nitrogen Oxides Over Ni/H-BEA Catalysts In Lean-Burn Conditions

Selective catalytic reduction (SCR) will be the mainstay for nitrogen oxides (NOx) removal from lean-burn conditions, and zeolite-based catalysts are considered to be SCR catalysts with prospective. In this work, we developed a series of Ni/H-BEA and Ni-Fe/H-BEA catalysts by impregnation. Then the catalytic activities of these catalysts for NH3-SCR, HC-SCR, and NTP-assisted C3H8-SCR processes were carried out under a lean-burn condition. The main conclusions are as follows:In the NH3-SCR system, the 3%Ni/H-BEA showed the highest activity among all samples, its optimum reaction temperature range from 350 to 500℃. The activity of Ni/H-BEA declined as the GHSV increased from 20000 to 100000 h"1. NOx conversion increased as the NH3/NO molar ratio increased, the most suitable NH3/NO molar ratio was 1. The effect of oxygen concentration (4-10%) on catalytic activity of Ni/H-BEA was insignificant. The activity of Ni/H-BEA was inhibited in the presence of SO2 and H2O, mainly due to the ammonium salts formed on the catalyst.In the HC-SCR system, the C3H8-SCR activity was higher than the CH4-SCR activity over Ni/H-BEA. The addition of iron significantly lowered the optimum reaction temperature of Ni/H-BEA. The 3%Ni-1%Fe/H-BEA had the highest activity among samples with different bimetal loadings. The main active components over Ni-Fe/H-BEA were NiO andα-Fe203. The addition of iron increased the nickel dispersion on the surface of catalyst and the acidity as well. Oxygen played an important role in activating NO and propane during the C3H8-SCR reaction. The NOx conversions decreased as the initial NO concentration increased at all investigated temperatures except 300℃. NOx conversion increased as the C3H8/NO molar ratio increased, a complete conversion of NOx was achieved with C3H8/NO=1.25 at 300℃. The addition of iron to Ni/H-BEA notably improved the tolerance of SO2 and H2O.The synergetic effect between NTP and C3H8-SCR was obvious at low temperature, the inhibition of SO2/H2O was eliminated by the introduction of NTP.