Preeti Aghalayam

Global kinetic models capable of capturing experimentally observed features of catalytic reactions are vital in design and optimization studies. In this work, a detailed analysis of the selective catalytic reduction of NO and NO2, particularly in automotive exhaust control is undertaken. The prominent metal based catalysts for this reaction range from Pt, Au & Rh to cheaper options including Cu, Ag & Co supported on Al2O3, SiO2, and occasionally, zeolites. Here, we focus on Ag & Co supported on Al2O3 catalysts, and propose a computationally tractable kinetic model capable of capturing the observed SCR features across a range of catalyst synthesis and reactor operating conditions. In particular, the effects of metal loading on catalyst performance are closely examined. In SCR, an important aspect is the catalytic activity at higher inlet O2 concentrations. The global kinetic model proposed here is shown to predict the trends with respect to reactor temperature and inlet feed compositions (including O2), well, for both catalysts.

High surface area mesoporous solid support has attracted much interest in the development of cost-effective catalysts for NOx abatement at low temperatures. SBA-15, a high surface area mesoporous material, was employed in the preparation of Al, Ti, and Zr incorporated SBA-15 through a direct synthesis approach under long hydrothermal reaction conditions (100 °C for 72 h). Heteroatom incorporation facilitated change in the morphology and textural properties of the material and was applied as a catalytic supports in order to facilitate the development of a MnCu bimetallic catalyst by a facile conventional co-impregnation method. At temperatures as low as 260 °C, the catalyst that was developed displayed superior deNOx activity for SCR of NO with NH3. There have been various physicochemical studies undertaken on the catalysts that were prepared, such as XRD, XPS, BET, HR-SEM, and HR-TEM. The deNOx optimization and deNOx activity over the catalysts are discussed. The exceptional deNOx activity at low temperatures may be attributed to the rod-like morphology, extensive oxygen vacancies, and high ratio of Mn3+ + Mn4+/Mn on 10Mn4Cu/Zr-SBA-15 catalyst. Furthermore, the catalyst also displayed a synergetic interaction between the Mn and the Zr species on its surface, which contributed to the catalyst's superior catalytic recycle ability and its long-term stability on stream stability. A useful approach of preparation is provided in order to accomplish the industrial use of a bimetallic catalyst consisting of manganese and copper at a low cost.

The effect of inlet flow distribution on the performance characteristics of a catalytic converter is analyzed for two common inlet manifold designs. Three-dimensional steady-state computational fluid dynamics simulations are performed under isothermal and nonisothermal conditions for the entire converter comprising an inlet manifold, central monolith, and outlet section. The porous medium approximation is used for the catalytic monolith. The reaction mechanism for a diesel oxidation catalyst with five global reactions is employed. A parameter called the “flow distribution index” is defined in order to quantify the nonuniformity of the velocity profile within the monolith and hence analyze the effect of operating conditions for the two geometries. Under isothermal conditions, catalytic converters with straight and U-bend inlet manifolds behave similarly and closely match single channel predictions. However, under nonisothermal conditions, there is a considerable difference in performance between the two geometries because of temperature variations. The presence of heat effects in the nonisothermal case marginally improves the flow uniformity within the monolith. However, in the presence of heat effects, reactant conversion in the center of the monolith varies from the periphery and the single channel model slightly overestimates the conversion for both geometries.

Selective catalytic reduction of nitric oxide using ammonia in the presence of excess oxygen remains a major challenge. In the present work, we developed mesoporous Al-SBA-15 supported NiRu catalysts with a high surface area and ordered mesoporous structure. The monometallic Ni catalyst were prepared by the modified beta-cyclodextrin impregnation method by maintaining 1/50 mol of β-CD/Ni and bimetallic NiRu catalyst was prepared by maintaining constant loading of 8 wt% Ni with different wt%. loading of xwt% Ru (x = 2, 4, 6 and 8). The developed catalysts were characterized by XRD, N2 sorption, FT-IR, Py-IR, UV-DRS, HRSEM, HRTEM and XPS. The NH3-SCR efficiency of both monometallic (Ni) and bimetallic (NiRu) catalysts are discussed. Additionally, monometallic 8 wt% Ni and Ru supported catalysts have been also synthesized by the conventional impregnation method for purposes of comparison. The remarkable low-temperature NH3-SCR conversion (90.2% NO conversion at 300 °C) of 8Ru8Ni/Al-SBA-15 catalyst under excess oxygen condition (7%) and superior % promotion (87%) of ruthenium addition was demonstrated with excellent textural properties, stability and corroborated with the physicochemical properties of the catalyst.

Cu/ZnO/ZrO2/Al2O3 catalysts are widely explored for CO2 conversion to methanol due to their higher activity and stability. However, mechanistic understanding of the performance of such catalysts is lacking due to ambiguity on the actual active sites. This study focuses on unraveling the nature of different interfaces on Cu/ZnO/ZrO2/Al2O3 catalyst by coupling experiments, Density Functional Theory (DFT) simulations and a DFT-based reactor scale multi-site microkinetic model. Although DFT calculations suggested the ZrO2/Cu interface to be the CO2 adsorption site, the validated microkinetic model predicted the ZnO/Cu interface to be the crucial reaction center. Reaction pathway analysis showed that methanol is produced through the formate pathway near the reactor entrance, whereas, the carboxyl pathway dominates in the latter zones, emphasizing the occurrence of both CO2 and CO hydrogenation. This deeper understanding of the reaction behavior of such multicomponent catalysts will aid in designing better catalysts and optimizing reaction conditions and systems.

Ag/γ-Al2O3 is an effective catalyst for the selective reduction of NOx (SCR) using propylene as a reducing agent. The catalyst performance is greatly influenced by the synthesis procedure. Various methods for synthesis of Ag/γ-Al2O3 are analyzed, and their performance is examined via packed bed reactor experiments in this work. An optimal one-pot synthesis method, single-step sol–gel (SSG) synthesis, is explored systematically. The SSG-synthesized catalyst shows better performance than those prepared via wet impregnation. The influence of synthesis conditions, specifically pH, on the textural and morphological properties of the SSG-synthesized Ag/γ-Al2O3, and therefore the activity for hydrocarbon-based SCR in a packed-bed reactor, are analyzed using experiments and simulations. The optimized catalyst demonstrates excellent performance (90% NOx conversion) for NOx reduction under nominal operating conditions with a wide activity temperature window (300–600°C). The catalyst shows good time-on-stream performance and is effective at higher inlet oxygen concentrations and space velocities. A global kinetic model, which uses synthesis-pH-dependent parameters, is proposed, and its ability to predict the activities of these catalysts is validated.