Edwin S. Gnanakumar

γ-Al2−xMxO3±y (M = Ti4+ through Ga3+): potential pseudo-3D mesoporous materials with tunable acidity and electronic structure

A simple and highly efficient surfactant-free sol–gel process has been developed to obtain nanocrystalline mesoporous γ-Al2O3 and metal ion incorporated mesoporous γ-Al2O3 with general formula γ-Al2−xMxO3±y (where M = Ti4+ through Ga3+). Any one of the first row transition metal (TM) ions along with Ga3+ could be introduced into the γ-Al2O3 framework in a direct one-pot synthesis process. The generality of the present synthesis recipe for metal ion incorporation in γ-Al2O3 was demonstrated by preparation of an Al–Ga–M ternary oxide system with the metal ion composition of general formula Al9GaTM (TM = Ti4+ to Zn2+) and their characterization through various physicochemical and spectroscopic techniques. The mesoporous γ-Al2−xMxO3±y materials showed a BET surface area in the range of 200–400 m2 g−1 with a narrow pore size distribution. Wormhole mesoporosity makes the material pseudo-3D (p3D) with a small pore depth of few nm (<10 nm). Metal ions in γ-Al2O3 lead to changes in the acidity and electronic environment. XRD, TEM, and 27Al MAS NMR studies demonstrate that the sol–gel process and the disordered mesoporous structure allow Ga and TM ions to be highly distributed and integrated in the γ-Al2O3 framework. The efficacy of these materials in catalysis has been successfully evaluated for steam reforming of dimethylether: Ni, Cu and Zn containing Al9GaTM oxides showed high activity and stability. The smaller mesochannel depth (<10 nm) and pseudo-3D characteristics that arise due to the wormhole-type disordered mesoporous framework of these alumina materials facilitate mass transport through them without any leaching of metal ions out of the lattice and pore blocking during the reaction, which makes them attractive in catalysis. This preparation method is versatile enough to be used for a reproducible synthesis of metal ion incorporated mesoporous γ-Al2O3 by varying the metal content and their combinations, and it is expected that many other metal ions could be introduced into the lattice framework for a variety of applications by tuning acidity and electronic structure.

Role of Nanointerfaces in Cu‐ and Cu+Au‐Based Near‐Ambient‐Temperature CO Oxidation Catalysts

Disordered mesoporous Cu‐doped ceria‐zirconia (Cu0.1Ce0.85Zr0.05O2), and gold deposited (Au/Cu0.1Ce0.85Zr0.05O2) catalysts were synthesized and evaluated for CO oxidation. Onset of CO oxidation activity, and 50 % (100 %) CO2 formation occurs at room temperature (RT), and 77 (120)°C, respectively, with Cu0.1Ce0.85Zr0.05O2. A small amount of gold on Cu0.1Ce0.85Zr0.05O2 induces the sustainable oxidation catalysis around RT. Onset of copper reduction temperature decreases from 110 °C on Cu0.1Ce0.85Zr0.05O2 to 48 °C with Au/Cu0.1Ce0.85Zr0.05O2, highlighting the direct interaction between Cu and Au through a Cu–Au interface. Au particles with a (0 0 1) facet deposit on an oxygen‐deficient site of (1 1 1) facet of CeO2‐ZrO2. Any decrease in surface Cu‐content with increasing Au‐content further supports the Au‐Cu‐Ce/Zr interface interactions. Nanointerfaces of Au clusters on Cu next to oxygen‐deficient sites of CeO2‐ZrO2 facilitate all the elementary steps of the CO+O2 reaction to occur in close proximity at ambient conditions.

Mechanistic Aspects of Wet and Dry CO Oxidation on Co3O4 Nanorod Surfaces: A NAP-UPS Study

Catalytic activity, electronic structure, and the mechanistic aspects of Co3O4 nanorod (NR) surfaces have been explored for CO oxidation in dry and wet atmosphere using near-ambient pressure ultraviolet photoelectron spectroscopy. Presence of water with CO + O2 plummets the catalytic activity because of the change in the electronic nature from predominantly oxide (without water in feed) to a Co3O4 surface covered by a few intermediates. However, at ≥375 K, the Co3O4 surface recovers and regains the oxidation activity, at least partially, even in the presence of water. This is fully supported by the changes observed in the work function of Co3O4 under wet (H2O + CO + O2) conditions compared with dry (CO + O2) conditions. This study focuses on the comparative CO oxidation rate on Co3O4 NR surfaces and highlights the changes in the electronic structure that occur in the catalyst during the CO oxidation reaction.

Porous thin films toward bridging the material gap in heterogeneous catalysis

Abstract An attempt has been made to bridge the material gap, existing between ideal single crystals and real-world powder nanocatalyst employed in surface science and heterogeneous catalysis, respectively. Simple wet chemical method (sol–gel and spin-coating deposition) has been applied to make continuous Ce1 − xZrxO2 (x = 0–1) (CZ) thin films with uniform thickness (~40 nm) and smooth surface characteristics. Uniform thickness and surface smoothness of the films over a large area was supported by a variety of measurements. Molecular beam (MB) studies of O2 adsorption on CZ surfaces reveals the oxygen storage capacity (OSC), and sticking coefficient increases from 400 to 800 K. Porous nature of Ce-rich CZ compositions enhances O2 adsorption and OSC, predominantly due to O-diffusion and redox nature, even at 400 K. A good correlation exists between MB measurements made on CZ films for oxygen adsorption, and OSC, and ambient pressure CO oxidation on powder form of CZ; this demonstrates the large potential to bridge the material gap. CZ was particularly chosen as a model system for the present studies, since it has been well-studied and a correlation between surface science properties made on thin films and catalysis on powder CZ materials could be a litmus test. Graphical abstract Ambient catalysis on ceria-zirconia nanocatalyst correlates well with surface properties measured through molecular beam on thinfilm and close the material gap.

9-Fluorenemethanol: an internal electron donor to fine tune olefin polymerization activity

A new MgCl2 based molecular adduct has been synthesized with 9-fluorenemethanol (9FM) as a novel internal electron donor (IED), along with ethanol (EtOH) (MgCl2·n9FM·xEtOH). The above molecular adduct has been subjected to a variety of structural, spectroscopic and morphological characterization techniques. The results of the solid state (13)C CPMAS NMR technique suggests the coordination of 9FM to MgCl2. Observation of a low angle diffraction peak at 2θ = 5.7° (d = 15.5 Å) underscores the coordination of 9FM along the z-axis, and ethanol in the molecular adduct. Active Ziegler-Natta catalysts were prepared by two different synthesis methods; the conventional method to obtain a high surface area active catalyst, and other one with 9FM as an integral part of the active catalyst in order to study the influence of 9FM as an IED over the active sites. The active catalysts were also characterized thoroughly with different analytical tools. The XRD results show (003) facets of δ-MgCl2 (α-MgCl2) for the conventional (non-conventional) titanated catalyst. Results of the ethylene polymerization activity study reveals that the conventionally prepared highly porous active catalyst shows 1.7-2.5 times higher activity than the non-conventional prepared catalyst; however, the latter shows a low molecular weight distribution and confirms the role of the Lewis base as an IED.