(337t) Integration of Porous Materials in Environmental Catalysis: Addressing Challenges in Emission and Sustainable Processes

My primary research interests are to explore porous materials in the fields of heterogeneous catalysis and emission control systems. I have gained a deep understanding of synthesis techniques, including the development of novel strategies for porous material synthesis, and applied them in diverse catalytic systems such as environmental catalysis, biomass transformations, and emission control processes. I have developed my skills in characterizing materials using a range of techniques. In my recent work, I have extended my research area to emission control system, with a specific focus on NO_X emission reduction using selective catalytic reduction process. I have acquired extensive experience in this domain by evaluating the impact of poisoning originating from lubricating oil elements and diesel engine exhausts.

I am interested in a position that will allow me to leverage my extensive knowledge and expertise in material design for applied applications, with a particular focus on environmental catalysis.

Synthesis of Porous materials:

In porous materials, Zeolites play a pivotal role due to their versatile shape selectivity and framework stability. The ion-exchange property, high thermal stability, and high acidity make them prominent materials in a wide range of interdisciplinary research areas. Therefore, significant efforts are being made to prepare zeolites with different framework structures. Several top-down and bottom-up approaches have been developed utilizing soft and hard templates for the preparation of nanocrystalline zeolite/hierarchical zeolites. However, to develop the different zeolite frameworks using one mesoporous director is still challenging. Additionally, mesoporous organic structure directing agents often involves complex organic synthesis procedures. Therefore, it is crucial to establish a synthesis strategy that involves sustainable mesopore directing agents.

To address these challenges, different synthesis strategies involving sustainable mesoporous directing agents are proposed. A novel dual template-mediated, one step direct synthesis route is developed for the preparation of nanocrystalline zeolite of different framework structures such as ZSM-5, mordenite, and sodalite. Further, microporous-mesoporous-macroporous containing ZSM-5 and Beta were prepared by a simple, economical, and eco-friendly strategy by using starch as a biomass-based template. Mesoporous zeolites and tri-modal porous zeolites exhibited significantly improved catalytic activity and recyclability in diverse acid catalyzed reactions such as esterification, condensation, and Friedel crafts alkylation reactions involving bulky reactants/products as compared to commercial zeolites.

Functionalization of Porous Materials:

Applications of zeolites are limited to those reactions where redox active transition metal sites are required. Therefore, attempts have been made to develop a class of porous materials, known as metal–organic frameworks (MOFs). However, the catalytic applications of MOFs have witnessed only limited success due to their limited activity and structural un-stability. Hence, it is important to choose MOFs that are stable under liquid phase conditions in different solvents and under varied reaction conditions. Further, to increase the catalytic applications of MOFs, efforts have been made to prepare functional MOFs via new ligands or by post-synthesis modification.

In this study, I employed post synthesis modification methods to incorporate diverse active functional groups, such as nanoparticles and organic bases into the matrix of Cu/Zr based MOFs. These functionalized MOFs were investigated in coupling and condensation reactions for the preparation of industrially important synthetic intermediates. Furthermore, composite materials based on zeolite and MOFs were prepared to enable bifunctional catalysis in biomass transformation, especially in the synthesis of gamma γ-Valerolactone and 5-hydroxymethyl furfural, as well as CO₂ insertion reactions.

NO_X Emission reduction:

Cu-SSZ-13 has been widely used as a commercial catalyst for selective catalytic reduction (SCR) of NO_x in diesel engine exhaust systems. In real world applications, the deactivation of Cu-CHA via chemical poisoning derived from different exhaust gas components, originating from biodiesel and engine oils, can be a durability issue for SCR catalysts. Among the different deactivation modes, sulfur poisoning is the major one. Significant effort has been made to understand the mechanism of sulfur poisoning, and most studies have focused on the monomeric Cu species. The effect of sulfur poisoning on Cu dimer complexes though is still relatively unexplored.

Currently, I am investigating the effect of SO₂ species on the static Cu dimer species. CO titration experiments were performed to quantify the static Cu dimers presence in the catalysts before and after sulfur exposure. To count Cu dimers, it has been shown that Cu dimers can be titrated by CO via the following reaction.

[Cu²⁺-O^2--Cu²⁺]²⁺ + CO -----> CO₂ + 2Cu⁺

Furthermore, UV-Vis. analysis was employed to investigate the sensitivity of static Cu dimers to sulfur poisoning. Our preliminary finding reveals that the presence of SO₂ species has negative impact static Cu dimer species. Furthermore, the introduction of SO₃ to the sulfur feeds had an even more negative impact on SCR performance compared to SO₂ poisoning.

In addition to sulfur poisoning, we are also conducting investigations into the impact of lubricant oil elements on the performance of SCR catalysts. Our finding so far indicates that exposure to lubricant oils on Cu-SSZ-13 has a negative impact on SCR performance. Multiple exposures to oils results in sever poisoning of catalysts. High temperature experiments were run to evaluate if the catalysts could be regenerated after the oil exposures. These experiments confirmed that the accumulation of engine oil elements through multiple exposures can lead to the formation of stable species (metal oxides/ash/deposits) that cause irreversible poisoning.