Increasing Reaction Temperature (increasing + reaction_temperature)

Distribution by Scientific Domains


Selected Abstracts


Synthesis and Characterization of 1-, 2-, and 3-Dimensional Bimetallic UO22+/Zn2+ Phosphonoacetates

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2010
Karah E. Knope
Abstract Four bimetallic UO22+/Zn2+ phosphonoacetates have been prepared from hydrothermal reactions of uranyl nitrate, zinc nitrate, and triethyl phosphonoacetate. These compounds, (UO2)2(PPA)2(H2O)2Zn(H2O)64H2O (1), (UO2)4(PPA)2(HPPA)2Zn(H2O)65H2O(2), (UO2)2(H2O)2(PPA)2Zn(H2O)4 (3), and (UO2)2(PPA)2(HPPA)Zn2(H2O)23(H2O) (4), adopt 1-, 2-, and 3-dimensional architectures wherein the UO22+ cation exhibits coordination preference for the phosphonate over the carboxylate oxygen atoms. The Zn2+ metal centers show an increased degree of ligand coordination with increasing reaction temperature. At 120 C, compounds 1 and 2 are formed. These structures are 1- and 2-dimensional, respectively, and contain fully hydrated [Zn(H2O)6]2+ cations. At 150 C and 180 C, the HPPA ligand displaces H2O molecules from the inner Zn2+ hydration sphere and binds to the metal centers via a ,CO2H oxygen atom in 3 and both carboxylate and phosphonate oxygen atoms in 4. The overall Zn2+ reaction can be expressed by the equation Zn(H2O)62+ + HPPA [rlarr2] Zn(H2O)5(HPPA) + H2O. Presented here are the syntheses, structures, and characterization of these materials. [source]


Effect of pH of Medium on Hydrothermal Synthesis of Nanocrystalline Cerium(IV) Oxide Powders

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2002
Nan-Chun Wu
Well-crystallized cerium(IV) oxide (CeO2) powders with nanosizes without agglomeration have been synthesized by a hydrothermal method in an acidic medium by using cerium hydroxide gel as a precursor. The relationship between the grain size, the morphology of the CeO2 crystallites, and the reaction conditions such as temperature, time, and acidity of the medium was studied. The experiments showed that with increasing reaction temperature and time, the CeO2 crystallites grew larger. The crystallites synthesized in an acidic hydrothermal medium were larger and had a more regular morphology than the ones synthesized in a neutral or alkaline medium when the reaction temperature and time were fixed. The CeO2 crystallites synthesized in an acidic medium were monodispersed; however, there was vigorous agglomeration among the grains synthesized in a neutral or alkaline medium. It was demonstrated that the hydrothermal treatment was an Ostwald ripening process and the acidity (pH) of the used hydrothermal medium played a key role in the dissolution of smaller grains. It is proposed that the dissolution process can control the kinetics of the growth of larger grains. [source]


On the use of Cu catalysts for tailoring carbon nanostructures in alcohol-CVD

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11-12 2009
Ewa Borowiak-Palen
Abstract The use of the alcohol-chemical vapor deposition (A-CVD) process applying ferromagnetic catalyst mixes is a powerful technique for the synthesis of high purity single-, double- and multiwalled carbon nanotubes (MWCNTs). Here, we report on a systematic experimental study on the preparation route of carbon nanofibres (CNFs), bamboo-like carbon nanotubes (BMCNTs) with defined pocket size and mean diameter and MWCNTs. Copper serves as the catalyst. The morphology of the samples is controlled by the reaction temperature and the catalyst loading relative to the support content (MgO). A detailed analysis of the samples was achieved by electron transmission microscopy observations and Raman spectroscopy. Schematic illustration showing the carbon nanostructure evolution with increasing reaction temperature. [source]


Hydrogenation of naphthalene on nickel phosphide supported on silica

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2009
Xiaofei Zhang
Abstract Two series of silica supported nickel phosphide catalysts with different Ni/P atomic ratios of the precursors and loadings had been prepared by a temperature-programmed reduction of nickel phosphate. The resulting samples were characterized by means of N2 physorption and X-ray diffraction (XRD). The activities of the catalysts were measured for naphthalene hydrogenation (HYD) at 340 C and 4 MPa. The operating conditions of naphthalene HYD such as temperature, pressure and H2/liquor ratio were tested in detail. It is found that all the samples were active in this reaction and the sample which precursor with Ni/P = 1.25 and loading with 30 wt% displayed the highest catalytic activity and decalin selectivity. Naphthalene conversion and selectivity to decalin went through a maximum (100% and 83% at 340 C) with the increasing reaction temperature. Copyright 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source]