Preparation of Promoted Platinum Catalysts of Designed Geometry and the Role of Promoters in the Liquid-Phase Oxidation of 1-Methoxy-2-propanol

On-line characterization of platinum/graphite catalysts during liquid phase oxidations using cyclic voltammetry

“…Due to the low oxygen solubility of oxygen in water, circa 1 tool m-3, compared to the concentration of organic reactants which are usually in the order of 100 tool m-3 or higher, the oxygen containing species such as O and OH on the platinum surface can be removed by the organic reactant as soon as the stirring in the reactor is stopped, generally resulting in a zero-valent platinum surface. The only way to obtain insight in the oxidation state during the catalytic reaction is by measuring the open-circuit potential of the catalyst [9,10,28]. For fresh promoted catalysts, the degree of platinum coverage by tin-atoms can be calculated from the amount of hydrogen adatoms oxidized between 0 an 0.4 V vs. RHE before and after tin deposition:…”

“…The actual cause of activity loss depends on the type of reaction and the conditions applied. It seems that when the oxidation rate is controlled by the gas/liquid transfer of oxygen, the catalysts are more likely to be the subject of coverage by carbonaceous products than when the catalysts are applied in the kinetic regime [7][8][9][10]. This phenomenon is reported to be more pronounced when the catalyst is prereduced by the organic reactant [5,7].…”

“…Good results have been achieved with bismuth [7,9,10,16], lead [10,17] and tin [10]. Promoter metals can, however, also be the subject of corrosion [5], and optimal performance depends on the degree of coverage by the promoter metal [7,18].…”

“…during reaction. From this potential, the coverage of hydrogen and oxygen atoms can be evaluated [10,20], Cyclic voltammetry is a technique that can be considered as the liquid phase equivalent of the gas/solid temperature programmed techniques TPD, TPO and TPR [21,22]. The main parameter in cyclic voltammetry is the electric potential of the catalyst, which is changed linearly in time, just as the temperature is increased linearly in the temperature programmed techniques.…”

Gel-type ion exchange resin stabilized Pd-Bi nanoparticles for the glycerol oxidation in liquid phase

“…The promoter itself is inactive for the oxidation reactions, but when associated with the noble metal, it can considerably suppress the oxygen poisoning of the Pd surface [30], increase the reaction rate [33,34] and modify the selectivity [12,13,35]. Models proposed to interpret the role of promoters include the formation of i) a complexes between an α-functionalized alcohol, a surface Pt or Pd atom and a promoter [36], ii) a bifunctional catalysis [37], iii) an ordered alloy [34], iv) Bi may act as cocatalyst due to its higher affinity for oxygen and protect Pt or Pd from overoxidation [36] or v) as a homogeneous catalyst by leached promoter [31]. However, the most accepted role of Bi promotion is the geometric (blocking) effect of a fraction of active sites centered on the noble metal, since providing different coordination environment for substrate and in turn improving the catalytic performance of the original catalysts [12,38].…”