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HDC Activity (hdc + activity)

Distribution by Scientific Domains

Chemistry	100%

Selected Abstracts

Alumina-Supported Ni,Au: Surface Synergistic Effects in Catalytic Hydrodechlorination

CHEMCATCHEM, Issue 2 2009

Abstract Catalytic gas-phase hydrodechlorination (HDC) of 2,4-dichlorophenol (2,4-DCP) has been investigated over Ni/Al2O3 and Au/Al2O3 prepared by impregnation, and Au,Ni/Al2O3 prepared by reductive deposition of Au onto Ni. Catalyst activation by temperature-programmed reduction is examined and the activated catalysts are characterized in terms of H2 chemisorption, XRD and TEM-energy dispersive X-ray (EDX) measurements. Ni/Al2O3 (<1,10,nm) and Au/Al2O3 (<1,15,nm) exhibit a relatively narrow metal size distribution while Au,Ni/Al2O3 bore larger particles (1,30,nm) with variable surface Ni/Au ratios. Au/Al2O3 exhibits low H2 uptake and low HDC activity to generate 2-chlorophenol (2-CP) as the sole product. H2 chemisorption on Au,Ni/Al2O3 was approximately five times lower than that recorded for Ni/Al2O3 but both catalysts delivered equivalent initial HDC activities. Ni/Al2O3 exhibits an irreversible temporal deactivation where partial dechlorination to 2-CP is increasingly favored over full dechlorination to phenol. In contrast, thermal treatment of Au,Ni/Al2O3 in H2 after reaction elevates HDC activity with a preferential full HDC to phenol. This response is linked to a surface reconstruction resulting in a more homogeneous combination of Ni and Au. This result was also achieved by a direct treatment of Au,Ni/Al2O3 with HCl. A parallel/ consecutive kinetic model is used to quantify the catalytic HDC response. [source]

L-histidine decarboxylase as a probe in studies on histamine

THE CHEMICAL RECORD, Issue 6 2002
Takehiko Watanabe
Abstract Because the Falck-Hillarp formaldehyde fluorescence method, which was superbly applied to identify catecholaminergic and serotonergic neurons, is not applicable to histamine, the first author (T.W.) developed an antibody to L-histidine decarboxylase (HDC) for identification of the histaminergic neuron system in the brain. The anti-HDC antibody was of great use for mapping the location and distribution of this histaminergic neuron system. (S)-,-fluoromethylhistidine, a specific and potent irreversible inhibitor of HDC, was also very useful in studies on functions of the neuron system. The activity of HDC is increased by various agents, treatments, and physiological conditions. We found new compounds that increased HDC activity (i.e., tetradecanoylphobol acetate (TPA), other tumor promoters, and staphylococcal enterotoxin A); and using mast cell-deficient mutant (W/Wv) mice, we obtained evidence that this increase occurred in macrophages. To further characterize the mechanism of increases in HDC activity, the second author (H.O.) cloned human HDC cDNA and a human HDC gene. In studies on the regulation mechanism of the HDC gene, which is expressed only in limited types of cells such as mast cells, enterochromaffin-like cells in the stomach, cells in the tuberomammillary nucleus of the brain, and macrophages, CpG islands in the promoter region of the HDC gene were found to be demethylated in cells expressing the gene, whereas they are methylated in other cells that do not express the HDC gene. In collaboration with many other researchers, we developed HDC knockout mice. The resulting research is producing a lot of interesting findings in our laboratory as well as in others. In summary, HDC has been and will be useful in studies on functions of histamine. © 2002 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 2: 369,376, 2002: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.10036 [source]

Gas-phase hydrodechlorination of chlorobenzenes over silica-supported palladium and palladium,ytterbium,

APPLIED ORGANOMETALLIC CHEMISTRY, Issue 6-7 2003
Satyakrishna Jujjuri
Abstract A 5% w/w palladium loading on silica has been achieved via impregnation of the support with Pd(C2H3O2)2 and { (DMF)10Yb2[Pd(CN)4]3} , precursors to deliver monometallic (Pd/SiO2) and bimetallic (Yb,Pd/SiO2) catalyst systems respectively. The catalytic action of each has been assessed in the continuous gas-phase hydrodechlorination (HDC) of chlorobenzene (CB) and 1,2-dichlorobenzene (1,2-DCB) (T = 423 K, inlet chlorine/palladium mol ratio of 5 × 103 h,1) and the hydrogenation of benzene (T = 423 K, inlet C6H6/palladium mol ratio of 35 h,1). Activation of both catalysts delivered similar palladium crystallite size distributions with an average palladium diameter of 5,6 nm where the ytterbium component (in Yb,Pd/SiO2) was present as a thin surface coating. The Pd,Yb bimetallic exhibited significantly higher HDC and hydrogenation activities, the former manifested by significantly greater fractional dechlorinations and benzene selectivities/yields. Yb/SiO2 proved inactive in terms of promoting hydrogen scission or addition and the promotional effect of ytterbium in Yb,Pd/SiO2 is discussed in terms of electron donation and hydrogen transfer via surface YbH2. Under identical reaction conditions, a lower HDC activity was recorded for 1,2-DCB compared with CB, a response that is attributed to steric constraints allied to the deactivating effect of the second chlorine substituent. Both Pd/SiO2 and Yb,Pd/SiO2 exhibited a decline in HDC activity with time-on-stream, but the bimetallic was significantly more resistant to deactivation. Copyright © 2003 John Wiley & Sons, Ltd. [source]