Sn-modified Pt/SAPO-11 catalysts for selective hydroisomerization of n-paraffins

The hydroconversion of n-paraffins is a key reaction in hydrodewaxing of lubricating base oil. In this paper, we investigate the performance of Pt/SAPO-11 catalysts for isomerization of n-paraffins by the model compound of n-dodecane. Under this experimental condition, yields of feed isomers as well as cracking products are a function of the total n-dodecane conversion. Primary products are methylundecane while multi-brancheds and cracking products are formed in successive reactions. The result shows that the addition of Sn increases the selectivity for isomerization reaction. The most ideal experimental data for hydroconversion of n-dodecane is that the selectivity of isomerized products gets 90% when conversion of n-dodecane is 90% for the Sn-promoted Pt/SAPO-11 catalyst.

Stripping voltammetric determination of Pb(II) and Cd(II) based on the multiwalled carbon nanotubes-Nafion-bismuth modified glassy carbon electrodes

In this work, a new method for the simultaneous determination of Pb(II) and Cd(II) on the multiwalled carbon nanotubes (MWNT)-Nafion-bismuth modified glassy carbon electrode (GCE) using square-wave anodic stripping voltammetry has been studied. Scanning electron microscopy was used to investigate the characteristics of the MWNT-Nafion-bismuth modified GCE.

Electrochemiluminescence in the S2O82- system: Pt-Cd electrodes

The electrochemiluminescence (ECL) in the S2O82- system occurs under conventional cyclic voltammetry, when the Pt working electrode was coated with Cd elementary substance. The ECL mechanism was proposed, due to the reaction between the strongly oxidizing intermediate SO4 center dot- and the transitory production, CdO, generated by oxidation of Cd with SO4 center dot-. Moreover the ECL behavior was studied in different pHs and concentrations of S2O82- solution. It was showed that the ECL signal was strongest at pH 8.0, and its intensity increased with S2O82-. The experimental results verified well with the proposed ECL mechanism.

Large-scale, uniform DNA network on 11-mercaptoundecanoic acid modified gold (111) surface: Atomic force microscopy study

Large-scale, uniform plasmid deoxyribonucleic acid (DNA) network has been successfully constructed on 11-mercaptoundecanoic acid modified gold (111) surface using a self-assembly technique. The effect of DNA concentration on the characteristics of the DNA network was investigated by atomic force microscopy. It was found that the size of meshes and the height of fibers in the DNA network could be controlled by varying the concentration of DNA with a constant time of assembly of 24 h.

Investigation of oxygen- and hydrogen peroxide-reduction on platinum particles dispersed on poly(o-phenylenediamine) film modified glassy carbon electrodes

Composite membrane modified electrodes were prepared by electrochemical deposition of platinum particles in a poly(o-phenylenediamine) (PPD) him coated on glassy carbon (GC) electrodes. The modified electrodes showed high catalytic activity towards the reduction of oxygen and hydrogen peroxide. A four-electron transfer process predominated the reduction process. The pH dependence and the stability of the electrodes were also studied.

ELECTROCATALYTIC OXIDATION OF ASCORBIC ACID AT POLYANILINE FILM MODIFIED GLASSY CARBON ELECTRODES

A conducting polyaniline (PAn) film modified glassy carbon (GC) electrode was prepared by electrochemical polymerization. The electrochemical behavior of ascorbic acid (AH(2)) in aqueous solution at this PAn modified electrode was studied in detail. The experimental results show that PAn film modified electrode has good electrocatalytic activity on the oxidation of ascorbic acid in aqueous solution over a wide range of pH value, among which pH 4 is the optimum condition. The oxidation process of ascorbic acid at PAn film electrode can be regarded as an EC catalytic mechanism. The kinetic process of the catalytic reaction was investigated by rotating disk electrode (RDE) coated with PAn films. The rate constant of the catalytic reaction was evaluated. The catalytic peak currents are proportional to the concentrations tions of ascorbic acid in the range of 5 x 10(-2)-1 x 10(-6) mol . L-1. The PAn film elec trodes give very stable responce for the oxidation of ascorbic acid. The present investigation shows the posibility of using PAn film modified electrode for the determination of ascorbic acid.

Heterogeneous asymmetric hydrogenation of ethyl pyruvate on chirally modified Pt/Al2O3 catalyst with fixed-bed reactor

The enantioselective hydrogenation of ethyl pyruvate on the cinchonidine modified Pt/Al2O3 catalyst was investigated using a high-pressure reaction system with a fixed-bed reactor for the purpose to produce the,chiral product without separating the catalyst from the reaction system. The reaction was also investigated in a batch reactor for comparison. About 60% e. e. and 90% e. e. were obtained with the fixed-bed reactor and the batch reactor respectively, demonstrating the possibility for the heterogeneous asymmetric hydrogenation in the fixed-bed reactor. Some adsorbed chiral modifier, cinchonidine, can be slowly removed from the surface of Pt/Al2O3 under the continuous flow reaction, as a result, the e, e, values drops with the reaction time in the fixed-bed reactor. The enantio-selectivity is higher in the fixed-bed reactor, but lower in the batch reactor when ethanol was used as solvent than that when acetic acid as solvent. CO was used as molecular probe to characterize the adsorption of cinchonidine an the catalyst surface by IR spectroscopy, A red shift observed in IR spectra of coadsorbed CO with cinchonidine suggests that the cinchonidine adsorption is mainly through the pi -interaction with platinum surface and donating electron to the platinum surface.