In situ modification of a Pt catalyst supported on a mixed ionic-electronic conducting membrane

The electrochemical promotion of a platinum catalyst for ethylene oxidation on a dual chamber membrane reactor was studied. The catalyst was supported on a La_0.6Sr_0.4Co_0.2Fe_0.803 membrane. Due the supporting membrane's electronic conductivity it is possible to promote the reaction by controlling the oxygen chemical potential difference across the membrane. Upon establishment of an oxygen potential difference across the membrane, oxygen species can migrate and spillover onto the catalyst surface, modifying the catalytic activity. Initial experiments showed an overall promotion of approximately one order of magnitude of the reaction rate of ethylene, under an oxygen atmosphere on the sweep side of the membrane reactor, as compared with the rate under an inert sweep gas. The reaction rate can keep its promoted state even after the flow of oxygen on the sweep side was interrupted. This behavior caused further promotion with every experiment cycle. The causes of permanent promotion and on demonstrating controllable promotion of the catalytic activity are presented. This is an abstract of a paper presented at the AIChE Annual Meeting (San Francisco, CA 11/12-17/2006).

Electrochemical promotion of catalysis using solid-state proton-conducting membranes

A solid-state electrochemical reactor with ceramic proton-conducting membrane has been used to study the effect of electrochemically induced hydrogen spillover on the catalytic activity of platinum during ethylene oxidation. Suitable proton-conducting electrolyte membranes (Gd-doped BaPrO ₃ (BPG) and Y-doped BaZrO₃ (BZY)) were fabricated. These materials were chosen because of their protonic conductivity in the operational temperature region of the reaction (400-700 °C). The BZY-based electrochemical cell was used to investigate the open-circuit voltage (OCV) dependence on H₂ partial pressure with comparison being made to the theoretical OCV as predicted by the Nernst equation. Furthermore, the BZY pellets were used to study the effect of proton transfer of the catalytic activity of platinum during ethylene oxidation. The reaction was found to exhibit electrochemical promotion at 400 °C and to be electrophilic in nature, i.e. proton addition to the platinum surface resulted in an increase in reaction rate. At higher temperatures, the rate was not affected, within experimental error, by proton addition or removal. Under similar conditions, AC impedance showed that there was a large overall cell resistance at 400 °C with significantly decreased resistance at higher temperatures. It is possible that there could be a relationship between large cell resistances and the onset of electrochemical promotion in this system but there is, as yet, no conclusive evidence for this. © 2003 Elsevier B.V. All rights reserved.

Identifying the relative importance of stock characteristics

There is no consensus in the literature as to which stock characteristic best explains returns. In this study, we employ a novel econometric approach better suited than the traditional characteristic sorting method to answer this question for the UK market. We evaluate the relative explanatory power of market, size, momentum, volatility, liquidity and book-to-market factors in a semiparametric characteristic-based factor model which does not require constructing characteristic portfolios. We find that momentum is the most important factor and liquidity is the least important based on their relative contribution to the fit of the model and the proportion of sample months for which factor returns are significant. Overall, this study provides strong evidence to support that the momentum characteristic can best explain stock returns in the UK market. The econometric approach employed in this study is a novel way to assess relevant investment risk in international financial markets outside U.S. Moreover, multinational institutions and investors can use this approach to identify regional factors in order to diversify their portfolios.