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.

Deactivation mechanisms and anti-deactivation strategies of molecular sieve catalysts for NO_(x)reduction

Molecular sieve catalysts,owing to their unique chemical properties,are widely used as catalysts among various catalytic reactions.Abundant Br?nsted acid sites in molecular sieve catalysts usually enable active components to disperse well on the catalyst surface,and help to adsorb a large number of gas molecules to achieve maximum catalytic performance.Therefore,a variety of molecular sieve catalysts have been developed and used in the selective catalytic reduction of NO_(x)by NH_(3)(NH_(3)-SCR).For example,Cu molecular sieve catalysts such as Cu-SSZ-13 and Cu-SAPO-34 with wide temperature windows and stable structure are considered and applied as commercial catalysts for NO_(x)removal in diesel vehicles for a long time.Although molecular sieve catalysts possess many advantages,they still cannot avoid the serious deactivation caused by various factors in practical applications.In this review,reasons leading to the deactivation of molecular sieve catalysts for NO_(x)reduction in actual working conditions were concluded.The deactivation mechanisms of molecular sieve catalysts for NO_(x)reduction were analyzed and the corresponding anti-deactivation strategies were summarized.Finally,challenges and prospects of molecular sieve catalysts for NO_(x)reduction were also proposed.

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.

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.