Eun Duck Park

Oxidative carbonylation of phenol to diphenyl carbonate over supported palladium catalysts

Abstract Oxidative carbonylation of phenol to form diphenyl carbonate (DPC) was investigated in the multi-step electron transfer system containing homogeneous or heterogeneous palladium as the main component. Carbon-supported Pd catalyst showed a better DPC yield than the best homogeneous system with Pd(OAc)2 for the same amount of palladium. For the supported palladium catalyst, the hydrophobicity of the supports appeared to be critical for high yields of DPC. The palladium remained in the metallic state and dissolution into the reaction solution was, if there was any, negligible. Effects of promoters in carbon-supported Pd catalyst system were also examined.

Expression profile of nine novel genes differentially expressed in hepatitis B virus-associated hepatocellular carcinomas

Chronic hepatitis B virus (HBV) infection is known to be one of the major causes in the development of hepatocellular carcinoma (HCC), although the biomolecular mechanism(s) involved remain unclear. To identify the cellular gene(s) involved in HBV-associated hepatocarcinogenesis, we used the mRNA differential display method and examined three paired tumor and nontumor tissues, all of which had chromosomally integrated HBV-DNA through chronic infection. Using 240 different combinations of three one-base anchored oligo-dT primers and 80 arbitrary 13-mers, genes decreased or increased in expression more than twofold between each tumor tissue and its paired nontumor tissue were identified. Twenty-nine known genes and four novel genes were differentially over-expressed in the HCC tumor tissues. In contrast, 27 known genes and five novel genes were under-expressed in those tumor tissues. The nucleotide sequences of the nine novel gene fragments were determined and their expression patterns were examined in 40 HCC samples. HA61T2, PT18, HG63T1, and HG57T1 were preferentially over-expressed in 32 cases (80%, P<0.001), 24 cases (60%), 23 cases (57.5%) and 22 cases (55%) of the 40 tumor tissues, respectively. There was an increased frequency of HG57T1 over-expression in HCC patients with HBV-positive serology and low serum alpha-feto protein (AFP) levels (P<0.05). DNT10, PT8, PT19, ENT25 and HA6T4 were under-expressed in 26 cases (65%), 23 cases (57.5%), 21 cases (53%), 20 cases (50%) and 18 cases (45%) of the 40 tumor samples, respectively. There was a strong correlation of DNT10 under-expression with high serum AFP level in HCC patients, irrespective of HBV serology (P<0.01). HA6T4 was preferentially under-expressed in HCC tumors in patients with HBV-positive serology and high serum AFP levels (P<0.05). Thus, the functional analyses of the known and novel genes identified in this study should prove valuable to further understand the mechanism(s) of hepatocarcinogenesis.

Direct conversion of methane into oxygenates by H2O2 generated in situ from dihydrogen and dioxygen

Abstract Methane was directly converted into a methanol derivative and HCOOH by H2O2 generated in situ from H2 and O2 in the presence of Pd/C and Cu(CH3COO)2 catalysts. In this catalyst system, copper compound appeared to be essential for the activation of methane and the metallic palladium for the in situ generation of H2O2 from H2 and O2. This oxidation reaction does not appear to be a radical chain reaction.

Copper- and vanadium-catalyzed methane oxidation into oxygenates with in situ generated H2O2 over Pd/C

Abstract Copper- and vanadium-catalyzed oxidation of methane into methyl trifluoroacetate and formic acid with in situ generated H 2 O 2 from H 2 and O 2 over Pd/C was investigated in trifluoroacetic acid (TFA) and/or trifluoroacetic anhydride (TFAA) as a solvent. Metallic palladium was responsible for the in situ generation of hydrogen peroxide from dihydrogen and dioxygen. Divalent copper hydroperoxide and monoperoxomonovanadate, VO(O 2 ) + , seemed to be related to Cue5f8H bond activation. The radical chain reaction did not occur in either copper- or vanadium-catalyzed methane oxidation. However, methyl radical appeared to be produced in vanadium system but not in copper system.

Hydrodechlorination of CCl4 over Pt/γ-Al2O3: Effects of reaction pressure and diluent gases on distribution of products and catalyst stability

Abstract Pt/γ-Al2O3 catalysts were prepared by a wet impregnation method and applied for the hydrodechlorination of CCl4 around 400xa0K. The extent of catalyst deactivation was in line with the propensity of the formation of oligomers (mainly C2Cl4). Both catalyst stability and selectivity to CHCl3 were enhanced when the pressure was increased up to an optimum level. Above the optimum pressure, catalyst deactivation was accelerated with enhanced dimerization of abundantly adsorbed CCl4, due to the relatively hydrogen-deficient environment on the surface. Addition of diluent gases such as CH4, N2 improved the catalyst stability at pressurized reaction conditions. These gases adsorbed (albeit weakly) on platinum to reduce the selectivity to CHCl3, while improving the catalyst stability. The increased amount of hydrogen adsorbed on the platinum catalyst at high reaction pressures appeared to be the main factor for enhancement of selectivity to CHCl3 and catalytic stability.

Process development for low temperature CO oxidation in the presence of water and halogen compounds

Abstract A new process has been developed to oxidize CO at low temperatures ( 2 –CuCl 2 catalyst supported on carbon was successfully implemented to treat the oxidation reactor vent stream of a terephthalic acid plant that contained water, CH 3 Br and other organic compounds in addition to CO. The CH 3 Br remained intact during the treatment and did not deactivate the catalyst. In this catalyst system, palladium remained as a molecular Pd(II) species while solid Cu 2 Cl(OH) 3 was the active copper phase. The formation of stable Cu 2 Cl(OH) 3 was essential for activity and stability of the catalyst. After obtaining a stable catalytic activity for six months in a pilot plant test with a side stream of real vent gases, the first installation and operation of the process were made successfully to handle 50,000xa0Nm 3 /h of vent stream in a terephthalic acid plant.

Low temperature oxidation of CO over supported PdCl2-CuCl2 catalysts

PdCl2-CuCl2 catalyst supported on activated carbon was examined for the low temperature oxidation of CO. The catalyst developed in the present study was active and stable at ambient conditions if water were existing in the feed gas stream. The addition of Cu(NO3)2 into the PdCl2-CuCl2 catalyst significantly enhanced the CO oxidation activity. X-ray diffraction study revealed that the role of Cu(NO3)2 was to stabilize active Cu(II) species, Cu2Cl(OH)3, on the catalyst surface which maintains the redox property of palladium. When HC1 and SO2 were also existing in the feed, they easily inactivated the catalyst. It was found that HC1 and SO2 inhibited the formation of active Cu(II) species on the catalyst surface.

Easily separable molecular catalysis

Homogeneous metal catalysts offer greater selectivity and controllability because their molecular nature ensures that only one type of active site is present. However, the majority of large-scale, industrial chemical processes employs heterogeneous catalysts because of ease of their separation from products, thermal stability, and amenability to continuous processing. Heterogenization of homogeneous catalysts explores the cross-fertilization of two systems to combine most of their advantages. Some examples are discussed of heterogenized palladium complex catalysts applied for low-temperature CO oxidation, carbonylation for the synthesis of ibuprofen or naproxen, oxidative carbonylation for the synthesis of diphenyl carbonate, and functionalization of methane. There appears no significant change in reaction mechanisms when active centers are transferred from solution to the solid surface. In addition to the easy recovery, heterogenized homogeneous catalysts can have advantages in the productivity over homogeneous catalysts when a suitable support material is selected considering its hydrophilicity and surface reactivity.

Nature and role of active states of Pd and Cu in the oxidative carbonylation of phenols with Pd/C and cuprous oxide

Abstract Active states of palladium and copper for the oxidative carbonylation of phenol and bisphenol-A were investigated using X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) for Pd and Cu K -edges. The initial states of Pd and Cu were carbon-supported metallic Pd and cuprous oxide, respectively. During oxidative carbonylation, however, the metallic character of palladium was enhanced, as indicated by Pd K -edge XANES spectra taken before and after the reaction. Furthermore, Pdue5f8Pd coordination number increased from ca. 6.0 to 11.0, as determined by the quantitative EXAFS analyses of Pd K -edge. The initial crystalline cuprous oxide was converted by reaction with Bu 4 NBr into an unusual linear cuprous dibromide complex stabilized by tetrabutylammonium cation. Qualitative XANES and EXAFS analyses of Cu K -edge identified the structural and electronic configuration of the cuprous complex that was found to be the active main catalyst. There was a direct correlation between the formation of the cuprous complex and the catalytic activity and selectivity. Based on these results, a possible catalytic reaction scheme was proposed for the oxidative carbonylation of phenols with the catalytic system of Pd/C, an inorganic cuprous compound and Bu 4 NBr.

Effects of inorganic cocatalysts and initial states of Pd on the oxidative carbonylation of phenols over heterogeneous Pd/C

Abstract Effects of various metal complexes of Ce, Co, Mn, and Cu compounds and of initial states of Pd with different particle sizes were investigated on coupled oxidative carbonylations of bisphenol-A (BPA) and phenol over activated carbon-supported metallic palladium (Pd/C). In the presence of Ce(CH 3 COO) 3 as the cocatalyst, homogeneous Pd(CH 3 COO) 2 showed a better activity than Pd/C as the main catalyst. From screening of the various inorganic cocatalysts, Cu 2 O was chosen as the best partner with the activated carbon-supported metallic palladium. More interestingly, this heterogeneous Pd/C-Cu 2 O catalyst system was superior to the homogeneous catalyst systems such as Pd(CH 3 COO) 2 -Ce(CH 3 COO) 3 or Pd(CH 3 COO) 2 -Cu 2 O because it provided increased conversions of bisphenol-A and selectivities to desired para -position carbonylated products. The active phase of palladium in this catalyst system appeared to be metallic Pd, as evidenced by a stronger metallic character of palladium observed after the reaction with X-ray absorption of near edge structure (XANES) of Pd K-edge. In the presence of Pd/C, the nature of metal and ligand of the inorganic cocatalyst significantly affected the catalytic activity and selectivity. However, the initial state of supported Pd showed a negligible effect, even though the metallic character of Pd varied drastically due to increasing Pd loadings or reduction temperatures.