Effect of the Morphology of Pt Nanoparticles of Supported Pt Model Catalysts on CO Oxidation (original) (raw)
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The Journal of Physical Chemistry C, 2011
P roperties of the nanoparticles have been studied extensively both in catalysis and electrocatalysis. 1 In the latter case, these studies have been carried out with two main objectives: (i) understanding of fundamental aspects of the surface electrochemical activity and (ii) the development of new materials for practical applications, for example, in fuel cells. Despite the high cost, Pt and its alloys are among the most promising candidates both for cathode and anode catalysts in the fuel cell applications.
Journal of Molecular Catalysis A: Chemical, 2015
The dynamics of the CO adsorption on Pt nanoparticles deposited on TiO 2 (101) (pure, N-doped and/or reduced) have been investigated using UV-visible diffuse reflectance spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy and density functional theory. The results point to that N-doping and oxygen vacancies in the Pt/N-TiO 2 system should favour catalytic reactions in which CO conversion into CO 2 takes place mediated by support surface O atoms.
Applied Catalysis A: General, 2013
Particle size effect Carbon black Dispersion X-ray photoelectron spectroscopy a b s t r a c t Effect of Pt particle size on the catalytic activity of complete ethylene oxidation in the temperature range of 25-220 • C in fuel-lean conditions is investigated. Carbon black is used as a support for platinum nanoparticles of well-defined average sizes between 1.5 and 6.3 nm. The results demonstrate that ethylene oxidation on Pt/C is strongly size sensitive reaction. Thus, the smallest Pt/C-4 nanoparticles (1.5 ± 0.5 nm) exhibit much higher catalytic activity toward ethylene oxidation reaching 50% conversion at 88 • C compared to 164 • C for the largest Pt/C-1 (6.3 ± 0.5 nm) nanocatalysts. XPS shows that particle size decrease results in noticeable binding energy increase and Pt4f peak broadenings. This indicates that the electronic effect induced by small Pt nanoparticles might play a role in the observed increase in their activity toward C 2 H 4 oxidation.
The mechanistic role of platinum and precious metals in promoting cobalt hydrogenation catalysts of the type used in reactions such as Fischer− Tropsch synthesis is highly debated. Here we use welldefined monometallic Pt and Co nanoparticles (NPs) and CO 2 methanation as a probe reaction to show that Pt NPs deposited near Co NPs can enhance the CO 2 methanation rate by up to a factor of 6 per Co surface atom. In situ NEXAFS spectroscopy of these same Pt NP plus Co NP systems in hydrogen shows that the presence of nearby Pt NPs is able to significantly enhance reduction of the Co at temperatures relevant to Fischer−Tropsch synthesis and CO 2 methanation. The mechanistic role of Pt in these reactions is discussed in light of these findings. P latinum and other precious metals are known to promote cobalt catalysts for the reaction of CO and H 2 to hydrocarbons, known as Fischer−Tropsch synthesis. This reaction, initially developed by Franz Fischer and Hans Tropsch to the point of practical use in the early 20th century, is considered to be a viable option to partially replace crude oil derived transportation fuels, and therefore of considerable current interest. 1,2 Industrial Fischer−Tropsch synthesis now produces >200,000 barrels per day of synthetic oil. 1 Such catalysts have also been identified to be attractive as possible catalysts for CO 2 hydrogenation, 3,4 an analogous reaction that is desirable as a means of utilizing the greenhouse gas CO 2 to generate useful products. The latter is useful both for offsetting the cost of CO 2 capture and removing the need for subsequent CO 2 storage in CO 2 emission reduction schemes. 5 In either case, the role of Pt in promoting Co-catalyzed reactions of this type is generally not well understood, with a number of alternative explanations being offered for Pt's role. These can be classified as both structural and chemical effectsthe former changing the dispersion of the Co and the latter influencing the catalytic chemistry. 6 It has been postulated this could include intimate contact between the two metals modifying the local band structure, ensemble-type geometric effects, prevention of deactivation by carbonaceous deposits, and improvement in the reducibility of Co. 7−11 Interestingly for the present work, in a series of papers on Pd−Co sol−gel catalysts for CO hydrogenation, palladium is postulated to produce hydrogen that both facilitates Co reduction and participates in the reaction. 12−14 Considerable attempts have also been made using aberration corrected scanning transmission electron microscopy to establish the possible role of precious metals in these reactions. In the impregnated commercial-type catalysts studied, Pt appeared as a surface atomic species within Co particles, but notably also improved the apparent reducibility of Co particles containing no precious metal atoms, suggesting hydrogen spillover was occurring. 15 Although PtCo phases have been seen by X-ray diffraction, 10 no isolated Pt particles have been observed in studies on commercial-type catalysts. Nevertheless, it is useful for understanding the role of Pt to investigate what happens when isolated Pt particles are used as the promoter.
The Role of Organic Capping Layers of Platinum Nanoparticles in Catalytic Activity of CO Oxidation
Catalysis Letters, 2009
We report the catalytic activity of colloid platinum nanoparticles synthesized with different organic capping layers. On the molecular scale, the porous organic layers have open spaces that permit the reactant and product molecules to reach the metal surface. We carried out CO oxidation on several platinum nanoparticle systems capped with various organic molecules to investigate the role of the capping agent on catalytic activity. Platinum colloid nanoparticles with four types of capping layer have been used: TTAB (Tetradecyltrimethylammonium Bromide), HDA (hexadecylamine), HDT (hexadecylthiol), and PVP (poly(vinylpyrrolidone)). The reactivity of the Pt nanoparticles varied by 30%, with higher activity on TTAB coated nanoparticles and lower activity on HDT, while the activation energy remained between 27 and 28 kcal/mol. In separate experiments, the organic capping layers were partially removed using ultraviolet light-ozone generation techniques, which resulted in increased catalytic activity due to the removal of some of the organic layers. These results indicate that the nature of chemical bonding between organic capping layers and nanoparticle surfaces plays a role in determining the catalytic activity of platinum colloid nanoparticles for carbon monoxide oxidation.
Promotion Effects in the Oxidation of CO over Zeolite-Supported Pt Nanoparticles
The Journal of Physical Chemistry B, 2005
Well-defined Pt-nanoparticles with an average diameter of 1 nm supported on a series of zeolite Y samples containing different monovalent (H + , Na + , K + , Rb + , and Cs + ) and divalent (Mg 2+ , Ca 2+ , Sr 2+ , and Ba 2+ ) cations have been used as model systems to investigate the effect of promotor elements in the oxidation of CO in excess oxygen. Time-resolved infrared spectroscopy measurements allowed us to study the temperatureprogrammed desorption of CO from supported Pt nanoparticles to monitor the electronic changes in the local environment of adsorbed CO. It was found that the red shift of the linear Pt-coordinated CtO vibration compared to that of gas-phase CO increases with an increasing cation radius-to-charge ratio. In addition, a systematic shift from linear (L) to bridge (B) bonded CtO was observed for decreasing Lewis acidity, as expressed by the Kamlet-Taft parameter R. A decreasing R results in an increasing electron charge on the framework oxygen atoms and therefore an increasing electron charge on the supported Pt nanoparticles. This observation was confirmed with X-ray absorption spectroscopy, and the intensity of the experimental Pt atomic XAFS correlates with the Lewis acidity of the cation introduced. Furthermore, it was found that the CO coverage increases with increasing electron density on the Pt nanoparticles. This increasing electron density was found to result in an increased CO oxidation activity; i.e., the T 50% for CO oxidation decreases with decreasing R. In other words, basic promotors facilitate the chemisorption of CO on the Pt particles. The most promoted CO oxidation catalyst is a Pt/K-Y sample, which has a T 50% of 390 K and a L:B intensity ratio of 2.7. The obtained results provide guidelines to design improved CO oxidation catalysts.
Electrochimica Acta, 2009
Combining non-destructive, identical location-transmission electron microscopy (IL-TEM) with rotating disk electrode (RDE) measurements, the influence of different treatment procedures on the catalytic activity of carbon supported Pt nanoparticles is probed. IL-TEM shows that the treatment of the catalyst has only minor influence on its structure or the particle shape and size; in particular no treatment induced particle agglomeration is observed. At the same time, both CO stripping and CO bulk measurements are significantly influenced by the electrochemical treatment. In consistence with previous studies this can be explained by the removal of defects in the CO adlayer structure while cycling in CO saturated solution. In contrast, however, it is demonstrated that CO annealing has no impact on the oxygen reduction reaction in the mixed kinetic-diffusion control potential region.