Selective catalytic reduction challenges

Ever since the first study of metal-exchanged zeolites as new catalysts for selective catalytic reduction (SCR) of NOx with methane in the presence of oxygen was undertaken (Li and Armor, 1993), the simultaneous catalytic removal of NOx and CH4 at the exhaust of lean-bum natural gas engines has remained a challenge. 

The NOx reduction for the exhaust from lean-burn engine is one of the greatest challenges in environmental protection, and a lot of researchers have strived to develop more effective catalysts by many ways. Their efforts could be possibly categorized into four approaches (1) NOx direct decomposition, (2) selective catalytic reduction on NOx with hydrocarbons (HC SCR),... 

Supported metal oxides are currently being used in a large number of industrial applications. The oxidation of alkanes is a very interesting field, however, only until recently very little attention has been paid to the oxidation of ethane, the second most abundant paraffin (1). The production of ethylene or acetaldehyde from this feed stock is a challenging option. Vanadium oxide is an important element in the formulation of catalysts for selective cataljdic reactions (e. g. oxidation of o-xylene, 1-3, butadiene, methanol, CO, ammoxidation of hydrocarbons, selective catalytic reduction of NO and the partial oxidation of methane) (2-4). Many of the reactions involving vanadium oxide focus on the selective oxidation of hydrocarbons, and some studies have also examined the oxidation of ethane over vanadium oxide based catalysts (5-7) or reviewed the activity of vanadium oxide for the oxidation of lower alkanes (1). Our work focuses on determining the relevance of the specific oxide support and of the surface vanadia coverage on the nature and activity of the supported vanadia species for the oxidation of ethane. 

The last section (19.6) is focused on the commercial potential and perspectives of using metal ammines in connection with, for example, polymer electrolyte membrane (PEM) and solid oxide fuel cells (SOFCs) as well as selective catalytic reduction (SCR)-DeNO c (NO c removal) in the transport sector, and it includes comments on the global availability and low cost of the carrier salts. This section also provides the authors perspectives on future trends and challenges in metal ammine research, along with links to the interested reader for further information on key articles, companies and websites. 

We have successfully demonstrated the principle of selective catalytic reductive deoxygenation of vicinal diols. The challenges inherent to this transformation have hindered development of carbohydrate-based organic feedstock chemistry. While there remain aspects of our chemistry that keep it a laboratory methodology, there is now a clear route to development. 

In fact, the selective catalytic removal of NO in presence of excess oxygen remains a challenge. Most of the cunent studies involve C1-C4 hydrocarbons as reductants and zeolites as catalysts, among which Cu-exchanged MFI zeolites are considered as one of the most active [2]. The reductant shows a complex influence in this reaction it has been thus reported that a Cu/Zr02 catalysts are active with pro-pene but show low activity with propane as reductant [3]. For a practical use reduction by higher alkanes would be attractive, siiKe it would be easier to handle in a vehicle. 

Selectivity in catalytic oxidation/reduction and acid-base reactions has been a long-term challenge in the catalysis field. While it has been recognized that the control of molecular activation and reaction intermediates is critical in achieving high selectivity, this issue has not been adequately addressed and is a serious challenge to the field. 

The use of supported mixed oxides in both catalytic combustion and NO reduction are challenging applications. In the case of high-temperature catalytic combustion there is an unsatisfied need to obtain solids able to maintain high combustion activity during extended operation, i.e., high-surface-area structurally stable solids. Another hot subject that deserves exploration is the use of washcoated highly dispersed mixed oxides for the selective reduction of NO with CO and hydrocarbons. These studies should be conducted in the presence of both SO2 and H2O to evaluate the potential practical application of these catalysts. 

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