Nanosphere Catalyst Research Articles

One-step pyrolysis process to synthesize dispersed Pt/carbon hollow nanospheres catalysts for electrocatalysis

An effective method for loading Pt nanoparticles on monodispersed hollow carbon nanospheres by one-step pyrolysis of polystyrene spheres (PS) adsorbed with platinum (IV) ions was developed. The polystyrene spheres were firstly enwrapped with a layer of sucrose and cetyltrimethyl ammonium bromide (CTAB) micelles. Adsorption of platinum (IV) ions onto the polystyrene spheres was carried out via electrostatic interaction between the negatively charged platinum salt and the positively charged amino group in the CTAB. Pyrolysis of the PS-Pt (IV) precursors at 600 °C under nitrogen atmosphere resulted in the simultaneous decomposition of the sucrose to carbon and the adsorbed platinum complex to metallic Pt. During this process the polystyrene spheres was removed and hollow sphere of PtC formed. Nanocomposites of hollow carbon nanospheres with different platinum loading were synthesized and their electrocatalytic activity was evaluated using methanol as a model molecule. Results showed that the as-prepared hollow carbon nanospheres supported platinum catalysts have high electrocatalytic activity and long-term stability towards the oxidation of methanol. The present method is promising for the fabrication of carbon supported platinum catalysts for the direct methanol fuel cell.

Catalytic reduction of nitrate on Pt-Cu and Pd-Cu on active carbon using continuous reactor: The effect of copper nanoparticles

The increasing pollution of natural sources of drinking water encourages the development of new emerging technologies and processes for water remediation. This work deals with the study of catalytic reduction of contaminated waters containing nitrates (60ppm) in a continuous reactor working at room temperature and atmospheric pressure and using hydrogen as reducing agent. Optimal proportions of Pt-Cu and Pd-Cu in bimetallic catalysts on activated carbon, obtained by wetness impregnation, have been found. Besides, novel catalysts obtained from copper nanoparticles doped with Pd or Pt and supported on activated carbon, have also been studied. For all catalysts the Pt-Cu pair seems to be more selective in the transformation of the nitrates ions to nitrogen compared to Pd-Cu pair. Furthermore, considering the noble metal amount, the bimetallic nanosphere catalysts are more active (between 20 and 50) than the impregnated ones. The catalysts have been characterized by hydrogen chemisorption, BET, X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analysis. During the reaction, a considerable amount of the noble metal in its oxidised form has been detected. Based on this result an additional step to the generally accepted reaction mechanism of the nitrate reduction has been proposed.

Kinetics of liquid phase hydrochlorination of acetylene in presence of cuprous chloride

In this study, we propose gold-intercalated ordered mesoporous carbon nanosphere catalysts in which gold nanoparticles are reduced by high-temperature carbonization of the carbonaceous matrix to catalyze the selective hydrogenation of aromatic nitro compounds. A spherical morphology of particles with size approximately 90 nm and ordered mesoporous arrays was clearly observed on the surface in the high-resolution scanning electron microscopy images. The X-ray photoelectron spectra and transmission electron microscopy images showed that the dispersed metallic gold nanoparticles (2.8 nm in diameter) were intercalated into a carbon framework. The IR spectra for CO chemisorption suggested the involvement of neutral gold atoms in a low-coordination state in clusters or a stepped surface. The gold nanocatalysts intercalated into the nanospherical mesoporous carbons exhibited high activity and selectivity for the hydrogenation of nitroarenes to the corresponding amines, using H2 as a reduction agent. The initial reaction rate reached 12.7 and 6.5 min−1 in the hydrogenation of p-chloronitrobenzene and 4-nitrophenol, respectively. This catalytic performance was retained for more than five catalytic runs with no obvious activity loss or gold leaching, indicative of high stability. The trapping test using a mercapto-functionalized SBA-15 solid revealed undetected soluble gold species in the reaction solution. The high activity and stability of the ordered mesoporous carbon nanosphere-supported gold catalysts was strongly correlated to the particle morphology change by thermal reduction, which can generate new low-coordinated gold atoms for intercalated gold NPs in the matrix.