Alkali-resistant NO_(x) reduction over FeVO_(4)/TiO_(2)catalysts via regulating the electron transfer between Fe and V

The presence of alkali metals in exhaust gas from stationary resources causes a grand challenge for the practical application of selective catalytic reduction(SCR)of NO_(x) with NH_(3).Here,alkali-resistant NO_(x) reduction has been successfully implemented via tailoring the electron transfer over Fe and V species on FeVO_(4)/TiO_(2)catalysts.The strong interaction between Fe and V induced electron transfer from V to Fe and strengthened the adsorption and activation of NH_(3)and NO over active VO_(x) sites.In the presence of K_(2)O,the strong electron withdrawing effect of Fe offset the electron donating effect of K on the VO_(x) species,thus protecting the active species VO_(x) to maintain the NO_(x) reduction ability.The enhanced adsorption and activation of NH_(3) allowed SCR reaction to proceed via E-R mechanism even after K_(2)O poisoning.This work elucidated the electronic effects on the alkali metals resistance of traditional ferric vanadate SCR catalysts and provided a promising strategy to design SCR catalysts with superior alkali resistance.

NO_(x) reduction against alkali poisoning over Ce(SO_(4))_(2)-V_(2)O_(5)/TiO_(2) catalysts by constructing the Ce^(4+)-SO_(4)^(2−)pair sites

Commercial V_(2)O_(5)-based catalysts have been successfully applied in NH_(3) selective catalytic reduction(NH_(3)-SCR)of NO_(x) from power stations,but their poor alkali-resistance restrains the wider application in nonelectrical industries.In this study,NO_(x) reduction against alkali poisoning over V_(2)O_(5)/TiO_(2) is greatly improved via Ce(SO_(4))_(2) modification.It has been originally demonstrated that Ce^(4+)-SO_(4)^(2−)pair sites play crucial roles in improving NO_(x) reduction against alkali poisoning over V_(2)O_(5)/TiO_(2) catalysts.The strong interaction between V species and Ce sites of Ce^(4+)-SO_(4)^(2−)pairs triggers the reaction between NH_(4)^(+) species and gaseous NO via Eley-Rideal(E-R)reaction pathway.After K-poisoning,the SO_(4)^(2−)sites of Ce^(4+)-SO_(4)^(2−)pairs as protective sites strongly bond with K and thus maintain the high reaction efficiency via the E-R reaction pathway.This work demonstrates an effective strategy to enhance NO_(x) reduction against alkali poisoning over catalysts via constructing Ce^(4+)-SO_(4)^(2−)pair sites,contributing to developing alkali-resistant SCR catalysts for practical application in nonelectrical industries.

Unraveling SO_(2)-tolerant mechanism over Fe_(2)(SO_(4))_(3)/TiO_(2) catalysts for NO_(x) reduction

Developing low-temperature SO_(2)-tolerant catalysts for the selective catalytic reduction of NO_(x) is still a challenging task.The sulfation of active metal oxides and deposition of ammonium bisulfate deactivate catalysts,due to the difficult decomposition of the as-formed sulfate species at low temperatures(<300℃).In recent years,metal sulfate catalysts have attracted increasing attention owing to their good catalytic activity and strong SO_(2) tolerance at higher temperatures(>300℃);however,the SO_(2)-tolerant mechanism of metal sulfate catalysts is still ambiguous.In this study,Fe_(2)(SO_(4))_(3)/TiO_(2) and Ce_(2)(SO_(4))_(3)/TiO_(2) catalysts were prepared using the corresponding metal sulfate salt as the precursor.These catalysts were tested for their low-temperature activity and SO_(2) tolerance activity.Compared to Ce_(2)(SO_(4))_(3)/TiO_(2),Fe_(2)(SO_(4))_(3)/TiO_(2) showed significantly better low-temperature activity and SO_(2) tolerance.It was demonstrated that less surface sulfate species formed on Fe_(2)(SO_(4))_(3)/TiO_(2) and Ce_(2)(SO_(4))_(3)/TiO_(2).However,the presence of NO and O_(2) could assist the decomposition of NH_(4)HSO_(4) over Fe_(2)(SO_(4))_(3)/TiO_(2) at a lower temperature,endowing Fe_(2)(SO_(4))_(3)/TiO_(2) with better low-temperature SO_(2) tolerance than Ce_(2)(SO_(4))_(3)/TiO_(2).This study unraveled the SO_(2)-tolerant mechanism of Fe_(2)(SO_(4))_(3)/TiO_(2)at lower temperatures(<300℃),and a potential strategy is proposed for improving the low-temperature SO_(2)-tolerance of catalysts with Fe_(2)(SO_(4))_(3) as the main active component or functional promoter.

Hydrothermally stable metal oxide-zeolite composite catalysts for low-temperature NO_(x) reduction with improved N_(2) selectivity

Development of hydrothermally stable,low-temperature catalysts for controlling nitrogen oxides emissions from mobile sources remains an urgent challenge.We have prepared a metal oxide-zeolite composite catalyst by depositing Mn active species on a mixture support of CeO_(2)/Al_(2)O_(3) and ZSM-5.This composite catalyst is hydrothermally stable and shows improved low-temperature SCR activity and significantly reduced N_(2)O formation than the corresponding metal oxide catalyst.Comparing with a Cu-CHA catalyst,the composite catalyst has a faster response to NH_(3) injection and less NH_(3) slip.Our characterization results reveal that such an oxide-zeolite composite catalyst contains more acidic sites and Mn^(3+)species as a result of oxide-zeolite interaction,and this interaction leads to the generation of more NH_(4)^(+)species bound to the Br?nsted acid sites and more reactive NOxspecies absorbed on the Mn sites.Herein,we report our mechanistic understanding of the oxide-zeolite composite catalyst and its molecular pathway for improving the low-temperature activity and N_(2) selectivity for NH_(3)-SCR reaction.Practically,this work may provide an alternative methodology for low-temperature NO_(x) control from diesel vehicles.