Influence of compressed carbon dioxide on hydrogenation reactions in cyclohexane with a Pd/C catalyst

The potential of CO2-expanded liquid media for chemical reactions has been examined in this work, using cyclohexane as a solvent and Pd/C as a heterogeneous catalyst for hydrogenation of styrene, citral, and nitrobenzene with H-2. The rate of hydrogenation reactions is increased, and the product selectivity is altered in the CO2-expanded cyclohexane phase. In the hydrogenation of citral, the selectivity to citronellal decreases with CO2 pressure, which changes from similar to 80% in the neat cyclohexane to similar to 65% at 16 MPa.

Hydrogenation of o-chloronitrobenzene to o-chloroaniline over Pd/C in supercritical carbon dioxide

Hydrogenation of o-chloronitrobenzene (o-CNB) to o-chloroaniline (o-CAN) with Pd/C has been investigated in supercritical carbon dioxide (scCO(2)) at 308 K. The influences of several parameters such as CO2, H-2 pressures, Fd metal particle size and reaction time have been discussed. CO2 pressure presented markedly effects on the reaction rate and product selectivity under the reaction conditions used, the selectivity to o-CAN at CO2 pressure from 8 to 13 MPa (supercritical region) was larger than that at CO2 pressure below 6 MPa (subcritical region).

Hydrogenation of cinnamaldehyde over Pt/RHCs in supercritical carbon dioxide - Influence of support pretreatment and phase behavior

The selective hydrogenation of cinnamaldehyde (CAL) was investigated using rice husk-based porous carbon (RHCs) supported platinum catalysts in supercritical carbon dioxide (SCCO2). The effects of surface chemistry treatment of the support and the reaction phase behavior have been examined. The Pt/H-RHCs (HNO3-pretreated) was more active for CAL hydrogenation compared with Pt/NH3 - RHCs (NH3 center dot H2O-pretreated). The Pt/RHCs catalyst exhibited a higher selectivity to cinnamyl alcohol (COL) compared with commercial catalyst of Pt/C, which is relative to the micro - mesoporosity structure of the RHCs.

Development of durable carbon black/titanium dioxide supported macrocycle catalysts for oxygen reduction reaction

Carbon black and titanium dioxide supported iron tetraphenylporphyrin (FeTPP/TiO2/C) catalysts for oxygen reduction reaction (ORR) were prepared by sol-gel and precipitation methods followed by a heat-treatment at temperatures of 400-1000 degrees C. The FeTPP/C and TiO2/C were also studied for comparison. The FeTPP/TiO2/C pyrolyzed at 700 degrees C exhibits significantly improved stability while maintaining high activity towards ORR in comparison with the FeTPP/C counterpart. The electrochemical study combined with XRD, XPS, and SEM/EDX analyses revealed that the appropriate dispersion of TiO2 on the surface of FeTPP/TiO2/C catalysts, which depending on heat-treatment temperature, plays a crucial role in determining the activity and stability of catalysts.

Alternating Copolymerization of Carbon Dioxide and Propylene Oxide Catalyzed by Cobalt Schiff Base Complex

Cobalt 2,4-dinitrophenolate (complex 1) based upon a N,N,O,O-tetradentate Schiff base ligand framework was prepared. X-ray diffraction analysis confirmed that complex 1 was triclinic species with a six-coordinated central cobalt octahedron in the solid. Asymmetric alternating copolymerization of carbon dioxide (CO2) with racemic propylene oxide (rac-PO) proceeded effectively by complex 1 in conjunction with (4-dimethylamino)pyridine (DMAP), yielding a perfectly alternating and bimodal molecular weight distribution PO/CO2 poly(propylene carbonate) (PPC) with a small amount of cyclic carbonate byproducts.

Carbon dioxide/propylene oxide coupling reaction catalyzed by chromium salen complexes

A series of chromium/Schiff base complexes N,N'-bis(salicylidene)-1,2-phenylenediamino chromium(III) X were prepared and employed for the alternating copolymerization of carbon dioxide with racemic propylene oxide in the presence of (4-dimethylamino)pyridine. The effect of the complex structure and reaction conditions on the catalytic activity, the poly(propylene carbonate)/cyclic carbonate (PPC/PC) selectivity, and the polymer head-to-tail linkages was examined. The experiments indicated that N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-phenylenediamino chromium(III) (NO3) exhibited the highest PPC/PC selectivity as well as polymer head-to-tail linkages and N,N'-bis(3,5-dichlorosalicylidene)-1,2-phenylenediimino chromiu(III) (NO3) possessed the highest catalytic activity among these chromium/Schiff base complexes. The structure of the produced copolymer was characterized by the IR, H-1 NMR, and C-13 NMR measurements.

Selective hydrogenation of maleic anhydride to gamma-butyrolactone in supercritical carbon dioxide

The reaction rates of the hydrogenation of maleic anhydride (MAH) and succinic anhydride (SAH) were significantly accelerated and the selectivity to gamma-butyrolactone (GBL) was enhanced largely when the reaction mixture was pressurized by a non-reactant of CO2. Above 99% selectivity to GBL was achieved in 14 MPa CO2, the superior selectivity in scCO(2) was attributed to that MAH and/or SAH could be extracted to CO2 phase and separated from H2O, the hydrolysis were thus minimized and so the selectivity to GBL was improved.

Selective hydrogenation of nitrobenzene to aniline in dense phase carbon dioxide over Ni/gamma-Al2O3: Significance of molecular interactions

The selective hydrogenation of nitrobenzene (NB) over Ni/gamma-Al2O3 Catalysts Was investigated using different media of dense phase CO2, ethanol, and n-hexane. In dense phase CO2, the total rate of NB hydrogenation was larger than that in organic solvents under similar reaction conditions; the selectivity to the desired product, aniline, was almost 100% over the whole conversion range of 0-100%. The phase behavior of the reactant mixture in/under dense phase CO2 was examined at reaction conditions. In situ high-pressure Fourier transform infrared measurements were made to study the molecular interactions Of CO2 with the following reactant and reaction intermediates: NB, nitrosobenzene (NSB), and N-phenylhydroxylamine (PHA). Dense phase CO2 strongly interacts with NB, NSB, and PHA, modifying the reactivity of each species and contributing to positive effects on the reaction rate and the selectivity to aniline. A possible reaction pathway for the hydrogenation of NB in/under dense phase CO2 over Ni/gamma-Al2O3 is also proposed.

Cyclization of citronellal to p-menthane-3,8-diols in water and carbon dioxide

A clean process has been developed for the synthesis of p-menthane-3,8-diols from cyclization of citronellal in CO2-H2O medium without any additives. With the addition of CO2, the reaction rate could be enhanced about 6 times for the cyclization of citronellal in H2O, because CO2 dissolved into water and formed carbonic acid inducing an increase of the acidity. Although, the reaction conversion in CO2-H2O is slightly lower compared to that obtained with sulfuric acid as catalyst, CO2-H2O could replace the sulfuric acid at a relative higher reaction temperature. The reaction kinetics studies showed that the hydration of isopulegols to p-menthane-3,8-diols is a reversible reaction. The equilibrium constant and the maximum equilibrium yield obtained in CO2-H2O at a range of CO2 pressures are similar to that with sulfuric acid catalyst.

Lead(IV) dioxide: an effective electron injection material to realize high-efficiency inverted top-emitting organic light-emitting diodes

Lead(IV) dioxide (PbO2) has been used as the electron injection layer (EIL) to realize high-efficiency inverted top-emitting organic light-emitting diodes (I-TOLEDs). It can be seen that the inserting of the PbO2 EIL significantly reduces operational voltage, thus greatly improving the current efficiency and power efficiency of fabricated I-TOLEDs. The 10-(2-benzothiazolyl)-1, 1, 7, 7-tetramethyl-2, 3, 6, 7-tetrahydro-1H, 5H, 11H-[1] benzopyrano [6, 7, 8-ij] quinolizin-11-one (C545T)-based I-TOLEDs with the PbO2 EIL exhibit a maximum current efficiency of 31.6 cd A(-1) and a maximum power efficiency of 14.3 lm W-1, which are both higher than 22.5 cd A(-1) and 5.4 lm W-1 of the I-TOLEDs with LiF as the EIL respectively. A detailed analysis with respect to the role mechanism of PbO2 in electron injection has been presented. The improvement in EL performance is attributed to the formation of the interfacial dipoles at the electrode interface due to charge transfer between PbO2 and Alq(3).

Carbon dioxide pressure induced heterogeneous and homogeneous Heck and Sonogashira coupling reactions using fluorinated palladium complex catalysts

The Heck reaction of iodobenzene and methyl acrylate was investigated with CO2-philic Pd complex catalysts having fluorous ponytails and the organic base triethylamine (Et3N) in the presence of CO2 under solventless conditions at 80 degrees C. The catalysts are not soluble in the organic phase in the absence Of CO2 and the reaction occurs in a solid-liquid biphasic system. When the organic liquid mixture is pressurized by CO2, CO2 is dissolved into the organic phase and this promotes the dissolution of the I'd complex catalysts. As a result, the Heck reaction occurs homogeneously in the organic phase, which enhances the rate of reaction. This positive effect Of CO2 pressurization competes with the negative effect that the reacting species are diluted by an increasing amount of CO2 molecules dissolved. Thus, the maximum conversion appears at a CO2 pressure of around 4 MPa under the present reaction conditions. The catalysts are separated in the solid granules by depressurization and are recyclable without loss of activity after washing with n-hexane and/or water.

Alternating copolymerization of carbon dioxide and propylene oxide by single-component cobalt salen complexes with various axial group

A series of single-component cobalt salen complexes, N,N'-bis(salicylidene)-1,2phenylenediamino cobaltIII X(X = Cl (1a), Br (1b), NO3 (1c), CF3COO (1d), BF4 (le), and N3 (If)) (SalphCoX), were prepared for alternating copolymerization of carbon dioxide and propylene oxide(PO) under mild condition. The axial anion X group of the SalenphCoX played important role in tailoring the catalytic activity, polymeric/cyclic carbonate selectivity, as well as stereochemistry of carbonate unit sequence in the polymer chain. SalenphCoX with an electron-withdrawing axial X group (complex 1c) was an ideal catalyst for the copolymerization of CO2 and PO to selectively produce polycarbonate with similar to 99% carbonate linkage and over 81% head-to-tail structure.

Templated assembly of mu(5)-CO32- decanuclear praseodymium and neodymium clusters through spontaneous fixation of atmospheric carbon dioxide

Reactions of Ln(III) acetate (Ln = Pr and Nd) and a polydentate Schiff-base in a mixture of methanol and acetonitrile resulted in the unprecedented assembly of novel Ln(10) aggregates containing two Ln(5) pentagons templated by mu(5)-CO32-, introduced via spontaneous fixation of atmospheric carbon dioxide. Magnetic analysis using an expression including the ligand field effects and molecular field approximation indicates weak antiferromagnetic coupling between the metal ions. This synthetic approach may represent a promising new route toward the design of new lanthanide clusters and novel multifunctional materials.

Synthesis of Ruthenium Dioxide Nanoparticles by a Two-Phase Route and Their Electrochemical Properties

Dissolvable, size- and shape-controlled ruthenium dioxide nanoparticles are successfully achieved through a two-phase route. The influence of reaction time, temperature, and monomer concentration and the nature of capping agents on the morphologies of nanoparticles are studied through transmission electron microscopy (TEM). A possible mechanism for the formation and growth of nanoparticles is also involved. X-ray powder diffraction (XRD) confirms the amorphous structure for as-prepared ruthenium dioxide nanoparticles. Samples are immobilized by simple dip-coating on a current collector, and the cyclic voltammetry measurement is utilized to investigate their electrochemical properties. The specific capacitance of one sample can teach as high as 840 F g(-1), which reveals the promising application potential to electrochemical capacitors.