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“Unprotected” Pt nanocrystals were modified with triphenylphosphine (PPh3), octadecylamine (ODA), poly(vinylpyrrolidone) (PVP), poly(vinyl alcohol) (PVA), and dodecanethiol (DT) to investigate the effect of protective agents on the intrinsic catalytic property of Pt nanocrystals. By evaluating the catalytic performance of these model catalysts for the hydrogenation of para‐chloronitrobenzene (p‐CNB), it was found that direct or indirect interaction between nanocrystals and protective agents imposed a great impact on the catalytic performance of the nanocrystals. Protective agents with different electron‐donating ability (PPh3, ODA, PVP, and PVA) directly altered surface electronic state of Pt nanocrystals to bring the surface Pt atoms into an electron‐rich state, which would exert influence on the hydrogenation course by changing the adsorption and the reactivity of reactant, intermediates, and products. In contrast, DT exerted an indirect influence on the Pt nanocrystals. The coordinated Pt atoms were oxidized by DT to generate cationic Pt species on the surface of nanocrystals, and the cationic species would simultaneously improve the hydrogenation rate and selectivity to para‐chloroaniline by polarizing the N=O bond in the −NO2 group of p‐CNB and altering the electronic state of Pt nanocrystals, respectively. This work provided further insights into nanocatalysis, which is helpful for further design and application of highly efficient nanocrystal catalysts.

Unprotected" metal and alloy nanoclusters prepared using the alkaline-ethylene glycol method (AEGM), stabilized by adsorbed solvent molecules and simple ions, have been widely applied in the development of high-performance heterogeneous catalysts and the exploration of the effects of metal particle size and composition, surface ligands of support, and modifiers on the catalytic properties of heterogeneous catalysts. The formation process and mechanism of such unprotected metal nanoclusters need to be further investigated. In this study, the formation process and mechanism of unprotected Pt and Ru nanoclusters prepared with AEGM were investigated by in situ quick Xray absorption fine spectroscopy (QXAFS), in situ ultraviolet-visible (UV-Vis) absorption spectroscopy, transmission electron microscopy, and dynamic light scattering. It was discovered that during the formation of unprotected Pt nanoclusters, a portion of Pt(IV) species was reduced to Pt(II) species at room temperature. With increasing temperature, Cl − coordinated to Pt ions was gradually replaced with OH − to form intermediate platinum complexes, which further condensated to form colloidal nanoparticles. Obvious scattering signals of the colloidal nanoparticles could be observed in the UV-Vis absorption spectra of the reaction system before the formation of Pt-Pt bonds, as revealed by QXAFS measurements. In situ QXAFS analysis revealed that Pt nanoclusters were derived from the reduction of Pt oxide nanoparticles. The average particle size of the nanoparticles obtained by heating the reaction mixture for 15 min at 80 C was 3.7 nm. High resolution transmission electron microscopy (HRTEM) images showed that the spacing between the crystal planes of the nanoparticles was 0.249 nm, indicating that the intermediate nanoparticles were platinum oxide. As the reaction proceeded, the average size of the nanoparticles decreased to 2.4 nm, and two types of nanoparticles were observed having different contrasts, corresponding to Pt metal nanoclusters standing on the intermediate metal oxide nanoparticles as confirmed by HRTEM images. When the reaction time was further extended, the average size of nanoparticles decreased to 1.4 nm, and the observed lattice spacing of the nanoparticles was the same as that of Pt( 111) crystal plane at 0.227 nm, indicating that the final products were Pt metal nanoclusters. In general, when metal oxides are reduced to metal nanoclusters, the density of the nanoparticles will increase, whereas the volume will decrease. Moreover, as shown in this study, the formation of multiple small metal nanoclusters standing on one metal oxide nanoparticle was also observed in TEM photographs. Thus, compared with the size of the initial nanoparticles, the average size of the final metal nanoclusters was significantly reduced. On the other hand, during the formation of unprotected Ru metal nanoclusters, Cl − in RuCl3 was first replaced with OH − to form Ru(OH) 6 3− , which further condensated to form Ru oxide nanoparticles, and unprotected Ru met...

Coupling conversion of CO32− to hydrocarbons with carbonation of ferrous species by CO2 leads to the generation of long-chain hydrocarbons.

Carbon supported Pt nanocrystals anchoring small Ru nanoclusters (Ru-co-Pt/C) could catalyze CO2 hydrogenation to form multi-carbon compounds (C2–C26) with an extraordinary C2+ selectivity of 90.1% at 130 °C.

The catalytic synthesis of multi-carbon alcohols (MCA, C n H 2n + 1 OH, n ! 3) and higher hydrocarbons from CO 2 and H 2 under low or even ambient temperature are realized for the first time over a prepared bimetallic catalyst composed of nanoparticles of Pt and Ru supported on Fe 3 O 4 (RuÀPt/Fe 3 O 4 ). At 40 8C, the selectivity for alcohols, MCA, and higher hydrocarbons reached 77.1 %, 4.5 %, and 19.5 %, respectively, while that for methane was only 3.4 % (carbon based). As revealed by isotope tracer experiments using O 18 labeled water, in the hydrogenation of CO 2 over RuÀPt/Fe 3 O 4 , MCA could form by catalytic hydrolysis of alkyl, a novel reaction pathway enabling the formation of MCA at low temperature, which is different from the previously reported one based on CO insertion at high temperature. It was discovered that in RuÀPt/Fe 3 O 4 , both Ru and Pt nanoparticles played catalytic roles in the reduction of CO 2 to CH x species and the carbon-carbon coupling reaction to form alkyl, while the catalytic hydrolysis of formed long-chain alkyl occurred on Pt nanoparticles. CO 2 is a cheap, nontoxic, and abundant carbon source. The rising concentration of CO 2 in the atmosphere has been causing serious problems such as the greenhouse effect and ocean acidification. Therefore, the conversion of surplus CO 2 to hydrocarbon or oxygenated hydrocarbon is a significant subject. [1][2][3][4][5][6][7][8][9][10][11][12][13] The development of new catalytic systems capable of realizing the conversion of CO 2 to multi-carbon products (hydrocarbons or alcohols) at low or even ambient temperature is an attractive subject because such systems will not only provide high value products by consuming CO 2 , but also avoid over-emission of CO 2 in the conversion process. MCA with 3-8 carbon atoms are not only liquid fuels but also widely used as fine chemicals or solvents in producing pharmaceuticals, polymers, surfactants, detergents, paints, and printing inks. [14][15][16] The conversion of CO 2 and H 2 to multi-carbon compounds (CCMC) should be an ideal CO 2 conversion route, and H 2 can be manufactured in a large scale from renewable energy sources, including solar energy, hydropower and biomass.Pioneering efforts have been made to create catalytic systems for the conversion of CO 2 to multi-carbon compounds. It was reported that higher hydrocarbons could be synthesized from CO 2 and H 2 at high temperature over some heterogeneous catalysts. Song reported a FeÀCo bimetallic catalyst which could catalyze the reaction of CO 2 with H 2 to produce higher hydrocarbons with a selectivity of 69 % and a small amount of MCA at 300 8C. [17] Recently, Ge and Sun prepared an efficient catalyst Na-Fe 3 O 4 /HZSM-5 which can catalyze hydrogenation of CO 2 to produce hydrocarbons containing 78 % of gasoline-range (C 5 -C 11 ) ones at a CO 2 conversion of 22 % at 320 8C. [18] Sun et al. reported that a bifunctional catalyst composed of indium oxide (In 2 O 3 ) and zeolites could catalyze the reaction of CO 2 with H 2 to produce gasoline-r...

A highly active catalyst for Fischer–Tropsch synthesis at 423 K was prepared, on which the adsorbed CO dissociated at 303 K.

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