H. R. Sahu

Bio: H. R. Sahu is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Combustion & Catalysis. The author has an hindex of 2, co-authored 2 publications receiving 56 citations.

Synthesis of CuO, Cu and CuNi alloy particles by solution combustion using carbohydrazide and N-tertiarybutoxy-carbonylpiperazine fuels

Abstract: Solution combustion synthesis has been used for the preparation of finely dispersed copper oxide, copper and copper–nickel bimetallic particles. The structure and morphology of the materials are studied by XRD and SEM techniques. The fuel content in the combustion mixture is found to be a crucial factor in controlling the formation of oxide and metal particles. Starting with copper nitrate trihydrate as oxidizer (O) and carbohydrazide as fuel (F), we obtained CuO (F/O=0.75–1), mixed valence copper oxides, CuO+Cu2O, (F/O=1.0–1.5) and metallic Cu (F/O=2). At very low fuel content (F/O=0.5), a polymeric phase of copper hydroxide nitrate is isolated from the combustion residue. We also report the use of a new organic fuel N-tertiarybutoxy-carbonylpiperazine for the preparation of Cu, Ni and CuNi bimetallic particles.

Vapor phase reduction of cyclohexanone to cyclohexanol on CexZr1-xO2 solid solutions

Abstract: Reduction of cyclohexanone to cyclohexanol using propane-2-ol as hydrogen donor has been carried out in vapor phase on CexZr1-xO2 solid solutions synthesized by ombustion synthesized at 302°C. The solid solutions around 0.4 mol% cerium content show better catalytic activity compared to pure ZrO2 and the selectivity to cyclohexanol is 98%. A moderate acid-base and good redox properties of CexZr1-xO2 solid solutions are seen to be responsible for the catalytic activity. A possible mechanism of hydride transfer has been proposed with cerium ions as promoters.

Ceria‐Based Solid Catalysts for Organic Chemistry

Abstract: Ceria has been the subject of thorough investigations, mainly because of its use as an active component of catalytic converters for the treatment of exhaust gases. However, ceria-based catalysts have also been developed for different applications in organic chemistry. The redox and acid-base properties of ceria, either alone or in the presence of transition metals, are important parameters that allow to activate complex organic molecules and to selectively orient their transformation. Pure ceria is used in several organic reactions, such as the dehydration of alcohols, the alkylation of aromatic compounds, ketone formation, and aldolization, and in redox reactions. Ceria-supported metal catalysts allow the hydrogenation of many unsaturated compounds. They can also be used for coupling or ring-opening reactions. Cerium atoms can be added as dopants to catalytic system or impregnated onto zeolites and mesoporous catalyst materials to improve their performances. This Review demonstrates that the exceptional surface (and sometimes bulk) properties of ceria make cerium-based catalysts very effective for a broad range of organic reactions.

Nanomaterials via solution combustion synthesis: a step nearer to controllability

Abstract: Solution combustion synthesis (SCS) is a worldwide adopted technique to synthesize nanomaterials, especially for oxides, because of its simplicity, energy and time-effectiveness, and low cost. The general difficulty encountered in SCS is the controllability over phases and morphologies of the products, which arises from the inherent rapid and uncontrollable combustion procedure. In this regard, the present work is devoted to review the recent progress on phase- and morphology-controlled SCS in detail. Besides the various metal oxides, SCS is now applicable to fabricate nanomaterials of metal phosphates, metal silicates, metal borates, metal sulfides, metals, and even alloys, through careful selection of solution compositions. Oxides with regular morphologies of flowers, belts, triangles, tubes, wires, and rods can be synthesized by SCS, in the presence of certain templates, or through a self-assembly procedure. The recent progress made on the synthesis of porous materials via SCS is summarized. SCS is also capable of growing metal oxide thin films at low temperatures, enabling the fabrication of low-cost and high-performance electronics on flexible plastic substrates.

Promoting effect of ceria on the physicochemical and catalytic properties of CeO2–ZnO composite oxide catalysts

Abstract: CeO2–ZnO composite catalysts prepared by amorphous citrate method have been investigated for cyclohexanol dehydrogenation and hydrogen transfer reactions. The precursors and catalysts have been characterized by TGA, CHN analysis, XRD, UV–vis–NIR diffuse reflectance, SEM and acid–base measurements. The amorphous precursors in citrate process contain one molecule of citric acid per Ce4+ or Zn2+ ions. Structural studies of composite oxides indicate the presence of individual oxide phases along with non-equilibrium solid solutions in a limited composition range. The composite oxides contain low coordination Ce3+ and Ce4+ sites. Cyclohexanone was obtained as main product for cyclohexanol transformation reaction carried out over these mixed oxide catalysts due to dehydrogenation on basic sites. The presence of ceria in the composite oxide enhances the surface area and acid–base properties facilitating the dehydrogenation process. At low ceria content, the CeO2–ZnO composite oxide catalysts show higher catalytic activity for both cyclohexanol dehydrogenation and hydrogen transfer reactions due to higher basicity, surface area and smaller crystallite sizes. Hydrogen transfer activity is found to be higher on CeO2(10%)–ZnO catalyst prepared by citrate method compared to the catalyst prepared by decomposition from acetate precursor. This study demonstrates the promoting effect of ceria in CeO2–ZnO catalysts for reactions involving acid–base sites.

The ethanol steam reforming over Cu-Ni/SiO2 catalysts: Effect of Cu/Ni ratio

Abstract: The operating conditions of SRE (steam reforming of ethanol) reaction were evaluated by thermodynamics, in considering of the application requirements in hydrogen concentration and energy consumption. Under the select operating conditions, 5% CuNi/SiO 2 catalysts with different Cu/Ni ratios prepared through incipient-wetness co-impregnation were tested for SRE. The catalysts were reduced with NaBH 4 at room temperature, and again reduced by H 2 at 623 K prior to temperature-programmed SRE testing to remove surface oxygen. The SRE reaction products indicate a reaction scheme involving ethanol dehydrogenation to acetaldehyde, wherein acetaldehyde steam reforming and acetaldehyde decomposition compete, and with subsequent CO conversion to CO 2 via water gas shift reaction. The catalysts with Cu/Ni ≥ 1 showed higher ethanol conversion, higher acetaldehyde conversion, higher selectivity of acetaldehyde steam reforming, and lower coking at temperatures below 673 K than the Ni-rich catalysts. Analyses by XRD, XPS, and EXAFS indicate that the Cu-rich catalysts had formed an alloy structure with Ni-enriched surface. The catalyst with Cu/Ni = 1 showed the highest performance in ethanol conversion, acetaldehyde conversion, the selectivity of acetaldehyde steam reforming, and the stability against particle sintering.

Fuel cell grade hydrogen production via methanol steam reforming over CuO/ZnO/Al2O3 nanocatalyst with various oxide ratios synthesized via urea-nitrates combustion method

Abstract: Hydrogen production via steam reforming of methanol has been studied over a series of CuO/ZnO/Al2O3 catalysts synthesized by the combustion method using urea as fuel. Furthermore, the effect of alumina loading on the properties of the catalyst has been investigated. XRD analysis illustrated the crystallinity of the Cu and Zn oxides decreases by enhancing alumina loading. BET showed the surface area improvement and FESEM images revealed lower size distribution by increasing the amount of alumina. EDX results gave approximately the same metal oxide compositions of primary gel for the surface of the nanocatalysts. Catalytic performance tests showed the well practicability of catalysts synthesized by the combustion method for steam reforming of methanol process. Alumina addition to the CuO/ZnO catalyst caused the higher methanol conversion and the lower CO generation. Among different compositions the sample with molar component of CuO/ZnO/Al2O3 = 4/4/2.5 showed the best performance which without CO generation at 240 °C its methanol conversion decreased from 90 to 60% after 90 h.