Recent progress in selective CO removal in a H2-rich stream

Preferential oxidation of CO (PROX) is an important reaction for removing small amounts of CO to a parts-per-million level from the hydrogen-rich stream, which will be ultimately supplied as a fuel to polymer–electrolyte membrane fuel cells. The key to the application of PROX is to develop a highly active and selective catalyst that operates well in a wide temperature window (e.g., 80–180 °C) and has good resistance to CO2 and steam. In the past decades, various catalyst formulations have been developed, among which platinum group metal catalysts, including Pt, Ru, and Ir—in particular, those modified with promoters such as alkali metals and reducible metal oxides—have received a great deal of attention for their significantly improved catalytic activities in the low-temperature range. In this minireview, the recent advances of the platinum group metal catalysts for the PROX reaction are summarized, including performances of unpromoted and promoted catalysts, reaction mechanisms, and kinetics. In addition...

Recent Advances in Preferential Oxidation of CO Reaction over Platinum Group Metal Catalysts

Research interest in bimetallic catalysts is mainly due to their tunable chemical/physical properties by a number of parameters like composition and morphostructure. In catalysis, numerous bimetallic catalysts have been shown to exhibit unique properties which are distinct from those of their monometallic counterparts. To meet the growing energy demand while mitigating the environmental concerns, numerous endeavors have been made to seek green and sustainable energy resources, among which hydrogen has been identified as the most promising one with bimetallic catalysts playing important roles. This tutorial review intends to summarize recent progress in bimetallic catalysts for hydrogen production, specifically focusing on that of reforming technologies as well as the relevant processes like water-gas shift (WGS) and CO preferential oxidation (PROX), and emphasizing on the fundamental understanding of the nature of catalytic sites responsible for generating high purity hydrogen and minimizing carbon monoxide formation. Meanwhile, some important synthesis and characterization methods of bimetallic catalysts developed so far are also summarized.

Bimetallic catalysts for hydrogen generation

A general two-step approach has been developed for the synthesis of very small and sintering-resistant bimetallic gold−silver nanoparticles on inert supports including commercial silica and alumina. In this approach, gold particles were formed in the first step on amino-functionalized silica or alumina support. Our density functional theory (DFT) calculations on selected model clusters show that the surface atoms of the gold particles formed in the first step carry slightly negative charges, which facilitates the subsequent Ag+ adsorption on the gold particle surface. Upon Ag+ adsorption and reduction by NaBH4 in the second step, specific nanoparticles with gold−silver alloy core and a silver nanoshell have been formed, as confirmed by our ultraviolet−visible spectroscopy (UV−vis), high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS) characterizations. Such particles have been found to be highly thermally stable, and their sizes remain substantially unchange...

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Synthesis of Thermally Stable and Highly Active Bimetallic Au−Ag Nanoparticles on Inert Supports

Modeling the electro-oxidation of CO and H2/CO on Pt, Ru, PtRu and Pt3Sn

Kinetic measurements on preferential CO oxidation in a H2-rich atmosphere (PROX) over a bimetallic, carbon supported
 PtSn catalyst reveal a high activity and selectivity already at low temperatures (0–80°C), superior to
 a commercial Pt/Al2O3 system The selectivity, though steadily decreasing with temperature, is remarkably
 high, 85% at low temperatures around 0–20°C, and even at 120°C it is, at 45%, still higher than that of standard Pt catalysts
 The observation that CO desorption is not rate limiting and that the selectivity decreases with increasing
 temperature, can be explained in a mechanistic model involving separation of the reactant adsorption
 sites (bifunctional surface), with competing CO and hydrogen adsorption on Pt sites/areas and oxygen adsorption predominantly on Sn sites and SnOx islands on/adjacent to the active PtSn particles The reaction takes place
 in a bifunctional way at the perimeter of these islands or by invoking a spill-over process This model
 is supported by CO temperature-programmed desorption (TPD), in situ
 diffuse reflectance IR Fourier transform
 spectroscopy (DRIFTS), and x-ray photon spectroscopy (XPS) measurements, which indicate that under reaction
 conditions the surface CO coverage on the metallic particles is high, but decreases with temperature, and that only part of the Sn is reduced, included in PtSn alloy particles, while another part is in an oxidic state, forming
 SnOx islands on and presumably also beside the active particles Its excellent performance makes PtSn an
 interesting catalyst for fuel gas purification in
 low temperature
 polymer electrolyte membrane
 fuel cell technology (PEM-FC)

https://pubs.rsc.org/en/content/articlepdf/2001/cp/b008062o

M. Hüttner

Papers

Bimetallic PtSn catalyst for selective CO oxidation in H2-rich gases at low temperatures