Critical Role of Mullite-type Oxides’ Surface Chemistry on Catalytic NO Oxidation Performance

Thampy, Sampreetha,Ashburn, Nickolas,Dillon, Sean,Liu, Chengfa,Xiong, Ka,Mattson, Eric C.,Zheng, Yongping,Chabal, Yves J.,Cho, Kyeongjae,Hsu, Julia W. P. American Chemical Society 2019 The Journal of Physical Chemistry Part C Vol.123 No.9

<P>By combining low energy ion scattering spectroscopy and density functional theory calculation, we study the surface composition and surface formation energy of AMn<SUB>2</SUB>O<SUB>5</SUB> (A = Sm, Bi) mullite-type oxides synthesized by different methods and their effects on NO catalytic performance. It is well-known that hydrothermal (HT) synthesis at low temperatures produces materials with higher specific surface areas (SSAs) compared with those synthesized by coprecipitation (CP) and high-temperature calcination; however, it is less clear how synthesis methods affect surface chemistry. We find that the NO oxidation performance of SmMn<SUB>2</SUB>O<SUB>5</SUB>-HT does not match the SSA increase when compared to the lower SSA SmMn<SUB>2</SUB>O<SUB>5</SUB>-CP. Combined experimental and theoretical investigation reveals that SmMn<SUB>2</SUB>O<SUB>5</SUB>-HT includes a higher fraction of inactive Sm-terminated surfaces, which explains its lower than expected activity. However, the surface chemistry change depends strongly on the A-site element. The exposed surfaces of BiMn<SUB>2</SUB>O<SUB>5</SUB>-CP are predominantly terminated by Bi and exhibit a very low activity, while BiMn<SUB>2</SUB>O<SUB>5</SUB>-HT contains active Mn-terminated surfaces. This study shows that catalytic performance is determined predominantly by surface chemistry, which depends critically on the A-site element and synthesis method and less by physical surface area.</P> [FIG OMISSION]</BR>

Thermal stability of mullite <i>R</i>Mn₂O₅ (<i>R</i>  =  Bi, Y, Pr, Sm or Gd): combined density functional theory and experimental study

Li, Chenzhe,Thampy, Sampreetha,Zheng, Yongping,Kweun, Joshua M,Ren, Yixin,Chan, Julia Y,Kim, Hanchul,Cho, Maenghyo,Kim, Yoon Young,Hsu, Julia W P,Cho, Kyeongjae IOP 2016 Journal of Physics, Condensed Matter Vol.28 No.12

<P>Understanding and effectively predicting the thermal stability of ternary transition metal oxides with heavy elements using first principle simulations are vital for understanding performance of advanced materials. In this work, we have investigated the thermal stability of mullite <I>R</I>Mn<SUB>2</SUB>O<SUB>5</SUB> (<I>R</I>  =  Bi, Pr, Sm, or Gd) structures by constructing temperature phase diagrams using an efficient mixed generalized gradient approximation (GGA) and the GGA  +  <I>U</I> method. Simulation predicted stability regions without corrections on heavy elements show a 4–200 K underestimation compared to our experimental results. We have found the number of <I>d</I>/<I>f</I> electrons in the heavy elements shows a linear relationship with the prediction deviation. Further correction on the strongly correlated electrons in heavy elements could significantly reduce the prediction deviations. Our corrected simulation results demonstrate that further correction of <I>R</I>-site elements in <I>R</I>Mn<SUB>2</SUB>O<SUB>5</SUB> could effectively reduce the underestimation of the density functional theory-predicted decomposition temperature to within 30 K. Therefore, it could produce an accurate thermal stability prediction for complex ternary transition metal oxide compounds with heavy elements.</P>

Stable and Active Oxidation Catalysis by Cooperative Lattice Oxygen Redox on SmMn₂O₅ Mullite Surface

Zheng, Yongping,Thampy, Sampreetha,Ashburn, Nickolas,Dillon, Sean,Wang, Luhua,Jangjou, Yasser,Tan, Kui,Kong, Fantai,Nie, Yifan,Kim, Moon J.,Epling, William S.,Chabal, Yves J.,Hsu, Julia W. P.,Cho, Kye American Chemical Society 2019 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.141 No.27

<P>The correlation between lattice oxygen (O) binding energy and O oxidation activity imposes a fundamental limit in developing oxide catalysts, simultaneously meeting the stringent thermal stability and catalytic activity standards for complete oxidation reactions under harsh conditions. Typically, strong O binding indicates a stable surface structure, but low O oxidation activity, and <I>vice</I><I>versa</I>. Using nitric oxide (NO) catalytic oxidation as a model reaction, we demonstrate that this conflicting correlation can be avoided by cooperative lattice oxygen redox on SmMn<SUB>2</SUB>O<SUB>5</SUB> mullite oxides, leading to stable and active oxide surface structures. The strongly bound neighboring lattice oxygen pair cooperates in NO oxidation to form bridging nitrate (NO<SUB>3</SUB><SUP>-</SUP>) intermediates, which can facilely transform into monodentate NO<SUB>3</SUB><SUP>-</SUP> by a concerted rotation with simultaneous O<SUB>2</SUB> adsorption onto the resulting oxygen vacancy. Subsequently, monodentate NO<SUB>3</SUB><SUP>-</SUP> species decompose to NO<SUB>2</SUB> to restore one of the lattice oxygen atoms that act as a reversible redox center, and the vacancy can easily activate O<SUB>2</SUB> to replenish the consumed one. This discovery not only provides insights into the cooperative reaction mechanism but also aids the design of oxidation catalysts with the strong O binding region, offering strong activation of O<SUB>2</SUB>, high O activity, and high thermal stability in harsh conditions.</P> [FIG OMISSION]</BR>

A Triple Continuum Transport Model for Colloid Migration in Fractured Formations

Vinish V. Nair,Santosh G. Thampi 대한토목학회 2012 KSCE Journal of Civil Engineering Vol.16 No.3

Transport of colloids in a fractured rock is strongly affected by alterations in the rock matrix, termed as fracture skin. In this work,a colloid transport model is developed to analyze its migration in fractured formations, based on the triple continuum approach,incorporating the fracture skin as the third continuum, besides the fracture and the rock matrix. The system of coupled partial differential equations governing transport in the fractured media is solved using a numerical model employing a fully implicit formulation and based on the finite difference method. Colloid migration in the fractured formation is investigated for both “with”and “without fracture skin” scenarios and for constant concentration and constant flux inlet boundary conditions. Simulations carried out using the model indicate that fracture skin can either enhance or retard colloid migration in a fracture depending on its properties. The porosity and diffusion coefficient of the fracture skin are found to be the critical fracture skin properties affecting the transport of colloids in a fractured medium.

Antitumor Actions of Imidazolyl-(4-oxoquinazolin-3(4H)-yl)-acetamides against Ehrlich Ascites Carcinoma

Nulgumnalli Manjunathaiah Raghavendra,Kanthappa Sathish Nagaranavile,Thampi Parameshwaran,Purvarga Mattada Gurubasavarajaswamy 대한약학회 2009 Archives of Pharmacal Research Vol.32 No.3

Breast cancer is the second most common type of cancer after lung cancer and the fifth most common cause of cancer death. Several structural classes of compounds were discovered against tumor, but many of the existing antitumor agents exhibit severe side effects. Hence there is a need to identify a novel chemical entity having a broad range of therapeutic activity with fewer side effects. In this direction, several imidazolyl-(4-oxoquinazolin-3(4H)-yl)-acetamides 1-4(a-d) were screened for their antitumor activity against Ehrlich Ascites Carcinoma (EAC) using in-vitro and in-vivo models. Compounds 4b, 4d, and 3a showed highly significant antitumor activity against EAC in comparison with vincristine as standard.

A Naturalistic Study of Treatment Outcomes with Aripiprazole in Young People with First Episode Psychosis

Seetal Dodd,Tom Callaly,Annette Thampi,Stephen McConnell,Paul Hantz,Derek Goodman,Kristy Kohlmann,Pedro Vieira da Silva Magalhães,Michael Berk 대한정신약물학회 2010 CLINICAL PSYCHOPHARMACOLOGY AND NEUROSCIENCE Vol.8 No.2

Objective: Adequate treatment of a first psychotic episode in young people is a difficult challenge but may be of critical importance for changing the course of psychotic illness. Pharmacotherapy is the standard treatment of psychosis, however there is a paucity of data specific to first-episode psychosis. Methods: In this study 12 young people who presented with a psychotic episode at a specialised early intervention service were commenced on treatment with aripiprazole. They were assessed at baseline and weeks 4, 6, 24 and 48 using a broad battery of outcome measures. Case notes were also examined. Results: Data was available for 6 participants at week 48, and of those, one remained on treatment with Aripiprazole at endpoint. Case histories were typified by presentations that included illicit substance use and treatments characterised by several changes in medications. No single treatment choice predominated. Most participants tolerated treatment and showed symptomatic improvement with individualised therapy. Conclusion: Most participants showed improvement during the treatment period. Aripiprazole was one of many medications used in this study and may have been useful for the treatment of some individuals with first episode psychosis.