Graphite-Supported Platinum Catalysts: Effects of Gas and Aqueous Phase Treatments

Abstract

The effects on the platinum particle diameter and the available platinum surface area of a graphite-supported platinum catalyst resulting from pretreatments and from performing a selective oxidation reaction are investigated. In the gas phase considerable catalyst sintering occurs only in the presence of oxygen at 773 K due to extensive carbon burn-off, whereas in an aqueous phase platinum particle growth is limited upon oxidative treatment. A hydrogen treatment in aqueous phase at 363 K causes platinum particle growth, aggregate formation, and covering of metal sites. These phenomena become more important with increasing pH. Platinum particle growth and aggregate formation are attributed to platinum particle rather than platinum adatom mobility and is caused by the destruction of the oxygen-containing surface groups on the graphite support, which serve as anchorage sites for the platinum particles. Site covering is caused by products originating from the graphite support, which are formed as a result of the reductive treatments. When performing the aqueous phase oxidation of methyl α-D-glucopyranoside at 323 K and a pH of 9, catalyst modifications are small under oxidative conditions. Exposure of the catalyst for several hours to methyl α-D-glucopyranoside under the same conditions but in the absence of oxygen causes site covering.

Investigation of the Oxygen Reduction Activity on Silver – A Rotating Disc Electrode Study

“…Thereafter the electrode tip was put in a light sheltered dryer under N 2 -atmosphere. Due to the hydrophilic nature of the oxidised GC reproducible smooth catalyst layers could be produced without the usage of any additives, furthermore the oxidation also enhances the sticking of the silver particles onto the GC [15,16].…”

Improving Heterogeneous Catalyst Stability for Liquid-phase Biomass Conversion and Reforming

“…It was reported that for platinum supported on graphite at high pH, under a hydrogen-rich atmosphere and at an elevated temperature, agglomeration of platinum could occur. [80] The reason was that removal of the graphite oxygen functional groups by hydrogen lead to lower adhesion and therefore higher mobility of the nanoparticles on the surface.…”

Electrochemical activity and stability of dealloyed Pt–Cu and Pt–Cu–Co electrocatalysts for the oxygen reduction reaction (ORR)

“…[6][7][8][9][10] increases catalyst particle size, reducing available electrochemical surface area (ECSA in m 2 g −1 cat ) and therefore should increase voltage loss (due to an increase in oxygen reduction overpotential). Furthermore, Pt dissolution or particle growth have been shown to be a function of potential [11,12], fuel cell operating temperature [7,8], relative humidity [7], and the presence of water [13][14][15][16], making it difficult to theoretically predict the resulting ECSA change over time in various Pt alloy systems. For Pt alloy nanoparticle catalysts, the issue of stability has often been convoluted due to the cross-comparison of alloys with various preparation conditions or particle size.…”