Preparation And Characterization Of Palygorskite Supported Transition Metal Oxides Catalyst For Low-temperature Selected Catalytic Reduction(SCR) Of NO By NH123

Nitrogen oxides (NOx) emitted from coal-fired power plants can cause acidrain, smog, and ozone depletion. It’s an important issue of air pollution contral forNOx prevention and removal in our country. Selective catalytic reduction(SCR) ofNOx is considered to be the most efficient and widely used technology for reducingNOx emissions from stationary sources. Nowadays, the vanadium-basedcommercial catalysts are widely used in SCR, which exhibit high catalytic activity,selectivity and stability. But the reaction temperature of commercial catalysts ishigh(300-400oC), so it need to locate the SCR unit upstream the electricprecipitation and flue gas desulfurization, the deactivation easily does occur byhigh concentration of SO2and dust. Moreover, there is no reserve space betweeneconomizer and air preheater of most existing power plant boilers in our country,which limit the spread of mainstream commercial catalysts. Therefore, developinglow temperature SCR catalysts to match our existing power plant is an importantdirection of flue gas purification.Natural palygorskite was used as single carrier or binder to mix with fly ash toprepare forming catalyst supports PG and FA-PG. SCR catalysts were preparedfrom various transition metal oxides (Fe, Cu, Mn, V, Ni) deposited by the solutionimpregnation. The SCR activity measurement was carried out in a fixed-bed quartzreactor. The catalysts were characterized by SEM, BET and TPD. It was concludedthat the Mn-based catalysts had the best low temperature SCR activity. Thendetailed studies of Mn(x)/PG/T and exploratory studies of Mn(x)-Fe(y)/FA-PGwere carried out.The results from optimizing the preparation parameters and operatingconditions of Mn(x)/PG/T catalysts showed that the Mn8/PG/300catalysts hadhigher low temperature SCR activity. More than95%NO conversion could beachieved over these catalysts at250oC under the condition of GHSV=4753h-1,NH3:NO=1:1,3%volO2. The characterization results from SEM, BET, XRD andTPD showed that the active center of catalysts was nano-MnO2, whoseconfiguration and dispersing was effected by Mn loading and calcination temperature. NH3adsorption was strong on the catalysts, but weak adsorbed NH3on Lewis acid sites mainly participated SCR reaction. NO adsorption was quiteweak on the catalysts. We preliminarily deduced that the SCR reactions on this typeof catalysts proceeded via an Eley–Rideal mechanism. NH3was absorbed on thesurface of catalysts and activated by MnOx. Then the SCR reaction occurredbetween adsorbed NH3and gaseous NO. The activation of weakly adsorbed NH3was a key step of SCR.This paper also studied the physical and chemical properties, SCR catalyticproperties of the binary catalysts which prepared by palygorskite-fly ash compositesupports supported iron and manganese. The results showed that when theFA:PG=1:1, co-supports exhibited good formability and mechanical strength.Fe-based catalysts Fe(y)/FA-PG showed poor low-temperature activity but somemiddle-temperature activity. Mn-based catalysts Mn(x)/FA-PG showed excellentlow–temperature activity. The catalytic activity of Fe-Mn binary catalysts wasbetter than mono-catalysts. The catalysts with Mn/Fe=4exhibited the bestlow-temperature SCR activity. The catalysts with Mn/Fe=9showed the widestreaction temperature range.