The selective catalytic reduction (SCR) of NOx with NH3 is considered to be the most promising technique for the efficient reduction of highly detrimental NOx (to N2) emitted from diesel engine vehicles. Amongst the various catalysts available for SCR, Fe- and Cu-zeolite catalysts are found to be highly stable and efficient towards maximum NOx reduction over a wide temperature range. Cu-zeolites are more active at low temperatures ( 350 oC) while Fe-zeolites are more active at high temperatures ( 400 oC). We carried out a comprehensive experimental and kinetic modeling study of key SCR reactions on Fe- and Cu-zeolite catalysts and present a detailed understanding of mass transfer limitations and kinetics and mechanistic aspects of various SCR reactions on these catalysts. Experiments carried out on monolith catalysts having different washcoat loadings, washcoat thicknesses and lengths indicate the presence of washcoat (or pore) diffusion limitations at intermediate to high temperature range in all the SCR reactions. A detailed analysis of the effect of temperature on the transitions between various controlling regimes (kinetic, washcoat diffusion and external mass transfer) is presented. Agreement in the differential kinetics studies of NO oxidation and standard SCR (NO + O2 + NH3) reactions indicates NO oxidation is the rate determining step for standard SCR. A detailed kinetic model capturing key features of all the SCR reactions is developed. This model accurately predicts the experimentally observed NOx conversions over a wide temperature range and different feed conditions. Finally, a systematic study of various SCR reactions is carried out on a combined system of Fe- and Cu-zeolite monolithic catalysts to determine if a high NOx conversion could be sustained over a wider temperature range than with individual Fe- and Cu-zeolite catalysts. Amongst various configurations, a dual-layer catalyst with a thin Fe-zeolite layer on top of a thick Cu-zeolite layer resulted in a very high NOx removal efficiency over a broad temperature range of practical interest. The kinetic model accurately captures the experimental data with a combined system of Fe- and Cu-zeolite catalysts and provides further insights into the catalyst arrangements for maximum NOx reduction efficiency.

This book is a printed edition of the Special Issue "Selective Catalytic Reduction of NO_x" that was published in Catalysts

The combination of NOx storage and reduction (NSR) and selective catalytic reduction (SCR) catalyst is a promising technology for the reduction of NOx emission from the exhaust of lean-burn or diesel engine vehicles. In the combined NSR/SCR system, NH3 generated in LNT during the rich phase is utilized in the SCR for additional NOx conversion. Therefore, the performance of the combined NSR/SCR depends strongly on the NH3 generating function of the NSR catalyst. Earlier studies show that lower Pt dispersion NSR catalysts give higher selectivity to NH3 making them ideal candidates for this particular application. In the first part of the work, we performed experiments on lower Pt dispersion catalysts to gain insights on the mechanistic effects of Pt dispersion on NOx conversion and selectivity. We also developed an improved crystallite-scale model of NSR that explicitly accounts for the crystallite scale gradients of the stored NOx. The calibrated model is able to capture the effects of Pt dispersion, rich phase duration and overall cycle time on cycle-averaged conversion and selectivity trends. In the second part, we carried out a simulation study of dual-layer NSR+SCR monolithic catalyst using (1+1)-D model of catalytic monolith with individually-calibrated global kinetic models. Simulations show that multiple combinations of catalyst loading can attain a given NOx conversion and N2 selectivity, and that there exists a loading of SCR washcoat for a given NSR catalyst for which the NOx conversion is maximum. Simulations of the dual-brick monolith are also performed to analyze the effects of catalyst architecture. Under identical conditions, the simulations show that dual-layer catalyst outperforms the dual-brick largely because of the better utilization of generated NH3. Finally, we performed an optimization study to identify optimal loading and configuration of combined Fe+Cu zeolite catalyst that gives overall high NOx removal efficiency over a broad range of temperature. Simulations suggest that the brick configuration in which Fe- brick is followed by Cu- catalyst is slightly better than dual-layer in which Fe- is coated on top of Cu- architecture. This is attributed to the diffusional limitations in the washcoat that is more pronounced in the dual-layer catalysts.

Advances and Technology Development in Greenhouse Gases: Emission, Capture and Conversion is a comprehensive seven-volume set of books that discusses the composition and properties of greenhouse gases, and introduces different sources of greenhouse gases emission and the relation between greenhouse gases and global warming. The comprehensive and detailed presentation of common technologies as well as novel research related to all aspects of greenhouse gases makes this work an indispensable encyclopedic resource for researchers in academia and industry.Volume 6 titled Methane, Nitrox Oxide, and Ozone Conversion and Applications studies the applications of any greenhouse gases (GHGs) other than carbon dioxide. This book reviews the applications of methane, nitrox oxide, and ozone. It investigates any valuable product fabricated with the inclusion of methane, nitrox oxide, and ozone. The book also reviews recent advances, the largest operating plants and pilots for methane conversion, the economic assessments and cost analysis, and environmental impacts and challenges that are faced when developing these processes - Introduces applications and chemicals produced from methane - Describes nitrous oxide conversion and applications - Discusses about various applications of ozone

The integrated LNT/SCR system is a promising technology for the reduction of NOx emission from the exhaust of lean-burn or diesel engine vehicles. The LNT/SCR operating concept involves the storage of NOx during the lean phase while unreacted hydrocarbons (C3H6, C2H4 etc.) and generated NH3 exit the LNT during the rich phase. In addition to NH3, olefinic hydrocarbons and/or partially oxidized species that break through the LNT may also adsorb on the SCR catalyst leading to additional NOx reduction by those species. In first part of the work, we performed bench-flow reactor and in-situ DRIFTS experiments to elucidate the propylene + NO + O2 reaction system on Cu-SSZ13 (chabazite) monolithic catalyst. Experiments were conducted under both steady state and transient conditions for application relevant feed conditions. Based on the bench-flow reactor studies and in-situ DRIFTS experiments a phenomenological reaction mechanism is proposed that involves reaction between oxygenates (partially oxidized hydrocarbon species) and NO to form isocyanates species ( -NCO), detected by DRIFTS which are further reduced to N2. The experimental work is followed by developing a mechanistic-based kinetic model is developed for selective catalytic reduction of NO with C3H6 on Cu chabazite (Cu-SSZ13) monolithic catalyst based on bench scale flow reactor studies and in-situ DRIFTS measurements. The kinetic model was developed in steps, starting with steady-state CO oxidation, followed by C3H6 oxidation, and then the C3H6 + NO + O2 reaction system. The models for CO+O2, C3H6+O2 and C3H6+NO+O2 were also validated using a new set of steady state experiments. The model provides insight about non-NH3 pathways (hydrocarbons, oxygenates, isocyanates etc.) for NOx reduction across the SCR. Finally, we developed a global kinetic model for co oxidation of CO and C3H6 over Pt/Al2O3 monolithic catalyst. The kinetic model developed is used to elucidate the dynamic and steady state hysteresis behavior observed during oxidation of CO+C3H6 mixture on Pt/Al2O3.