Catalyst In Supercritical Water Research Articles

Non-catalytic and selective alkylation of phenol with propan-2-ol in supercritical water.

Phenol can be alkylated with propan-2-ol without catalyst in supercritical water at 673 K with mainly ortho substituted alkylphenols being obtained and alkylation reaction rate increasing with increasing water density.

Organometallic chemistry in supercritical water: metallorganic products of the CpCo-catalyzed cyclotrimerization of acetylenes

Cyclotrimerization of t-butylacetylene or phenylacetylene with CpCo(CO)2 as catalyst in supercritical water yields the isomeric 1,3,5-tris-substituted- (1: R=Ph, 1a: R=but) and 1,2,4-tris-substituted benzene derivatives (2: R=Ph, 2a: R=but). The identification of the organometallic products obtained under these conditions is described. The formation of all possible isomers of the corresponding CpCo(bis-substituted-cyclobutadiene) (3, 4), CpCo(bis-substituted-CpCobaltacyclopentadiene) (5, 6, 7) and CpCo(bis-substituted-cyclopentadienone) (8, 9, 10) via GC-MS is reported. Two of three isomers of CpCo(bis-substituted-cyclopentadienone) (8, 9 (R=Ph), 8a, 9a (R=but)) were separated and characterized in substance. The structures of 8, 9, 8a and 9a were elucidated by single crystal X-ray diffraction. 8 crystallizes in the orthorhombic space group P212121 (No.19) with a=840.5(1), b=1105.9(2), c=1767.2(3) pm, V=1642.8(1)×106 pm3, Z=4, Dcalc=1.441 g cm−3, R1=0.0501 (I>3σ), wR1=0.0529 (I>3σ). 9 crystallizes in the orthorhombic space group Pna21 (No.33) with a=1086.7(1), b=4726.0(1), c=1668.5(1) pm, V=8427.3(1)×106 pm3, Z=20, Dcalc=1.404 g cm−3, R1=0.0705 (I>2σ), Rw=0.1321 (all data on F2). 8a crystallizes in the monoclinic space group P21/c (No. 14) with a=1441.6(3), b=1241.3(1), c=3672.6(6) pm, β=92.39(2)°, V=6566(2)×106 pm3, Z=16, Dcalc=1.280 g cm−3, R1=0.082 (I>2σ), Rw=0.144 (all data on F2). 9a crystallizes in the monoclinic space group P21/c (No. 14) with a=669.3(1), b=1335.7(1), c=1843.1(1) pm, β=94.78(1)°, V=1641.9(1)×106 pm3, Z=4, Dcalc=1.28 g cm−3, R1=0.0622 (I>2σ), Rw=0.1185 (all data on F2).

98/02885 High-pressure carbon dioxide removal in supercritical water gasification of biomass: Matsumura, Y. et al. Dev. Thermochem. Biomass Convers., 1997, 2, 864–877

Lignin, cellulose, and their mixture were gasified with a nickel catalyst in supercritical water at 673K and 25MPa. Gasification efficiency is low, but increases with the amount of the catalyst when softwood lignin is included in the feedstock. One possible mechanism is the catalyst being deactivated by tarry products from the reaction between cellulose and softwood lignin. Mixtures with hardwood and grass lignin were gasified much more easily. Sufficient amount of catalyst achieves high gasification efficiency even for the mixtures of cellulose and softwood lignin. Sawdust and rice straw were also gasified under the same condition. Interaction between each component was observed also for these real biomass feedstocks.

Water Density Effects on Homogeneous Water-Gas Shift Reaction Kinetics

Several years ago, using ab initio calculations, Melius et al. examined an interesting pathway for the homogeneous gas-phase water-gas shift reaction. They predicted that an enhancement in the rate of this reaction occurs at high water density due to changes in the generation of formic acid as an intermediate. To investigate this possibility, we have examined the conversion of CO and H2O to CO2 and H2 in the absence of a catalyst in supercritical water at conditions from 410 to 520 °C and 2.0−60 MPa. In these experiments, Raman spectroscopy produced in situ, real-time measurements of reaction rates in an optically accessible, constant-volume reactor. The most rapid homogeneous rate measured, at 59 MPa and 450 °C, corresponds to an effective first-order reaction rate constant of 0.0033 s-1. The data show that the measured reaction rates increase far faster than linearly as water density is raised above 0.35 g/cm3, and the pressure dependence of the rate constant indicates that the transition state is chara...

Oxidation of Phenol over a Transition-Metal Oxide Catalyst in Supercritical Water

The oxidation kinetics of phenol in supercritical water was examined in the presence of a solid catalyst consisting of supported copper, zinc, and cobalt oxides in an integrally operated fixed-bed reactor. For the conditions studied the rate of phenol disappearance was found to be well described by the Langmuir−Hinshelwood kinetic formulation, which accounts for the equilibrium adsorption of phenol and for dissociative oxygen adsorption processes to the different types of active sites and a bimolecular surface reaction between adsorbed species on adjacent active catalyst sites to be the controlling step. The apparent activation energy and the heat of phenol adsorption in the temperature range 400−440 °C were found to be 109 and 24 kJ/mol, respectively. The products identified in the effluent include dimers, single-ring compounds, organic acids, and gaseous end products. The involvement of a homogeneous−heterogeneous free-radical mechanism is indicated by the intermediates formed. The product distribution ...

Catalytic Oxidation in Supercritical Water

Recently, catalytic oxidation in supercritical water (SCW) has received considerable research attention. The major thrust of this current research effort is attributable to the rapid development of supercritical water oxidation (SCWO) as an innovative wastewater treatment technology. The incentives of catalyst-enhanced processes may include increased reaction rates, reduced residence times and temperatures, and optimized reaction pathways that are otherwise difficult to achieve through noncatalytic processes. However, the databases associated with the use of catalysts in SCWO are limited. The purpose of this paper is to (1) review catalytic enhancement and technology as related to SCWO; (2) analyze effects of SCW on catalysts and catalytic SCWO processes; and (3) present a catalyst development strategy for SCWO-related applications. Catalyst activity and stability (in terms of reaction kinetics, surface phenomena, and phase behavior of catalysts in SCW) are emphasized. The paper presents a useful database...