| CNT is a novel catalytic material with unique structure and properties and has drawn much attention as a potential catalytic material from a viewpoint of both fundamental research and industrial uses. It has been demonstrated that the use of CNTs as catalyst support can improve activity and selectivity in hydrogenation and electrocatalysis. Meanwhile, the oxygen-containing surface groups on CNTs also have received more and more attention, but only a few studies have been directed at elucidating the influence of the surface oxygen groups on the catalytic behavior of the CNTs-supported catalysts. In terms of current issues, we have developed oxidative treatments of CNTs with HNO3-H2SO4followed by thermal treatments to control the type of the surface oxygen groups or HNO3vapor treatment was applied for the oxygen and nitrogen functionalization of CNTs. Pt colloids have been synthesized at room temperature through simply introducing acetate to the aged ethylene glycol (EG) solution of H2PtCl6and the possible formation process was also discussed. Pt/CNTs was achieved through chemical reduction of H2PtCl6·6H2O by EG in the presence of NaOH. Selective hydrogenation of PA and1,5-COD were used as probe reaction to evaluate their catalytic performances. The main results are as follows.CNTs with different surface groups were achieved by oxidative treatments with HNO3-H2SO4followed by thermal treatments. The type and amount of surface oxygen functional groups on the CNTs can be tuned by thermal treatments at different temperatures in an inert atmosphere. Deposition of Pt particles onto CNTs was achieved through chemical reduction of H2PtCl6·6H2O by EG in the presence of NaOH. Both dispersion and sintering resistance of Pt nanoparticles were found to be a function of amount of oxygen surface groups on the carbon nanotubes, however, the amount of oxygen surface groups apparently did not affect the Pt loading on the CNTs. For the hydrogenation of PA, the TOF increased linearly when the Pt particle size increases, whereas the selectivity to ST did not depend on particle size.Gas-phase methods were applied for the oxygen and nitrogen functionalization of CNTs. The oxygen functionalization was performed by HNO3vapor treatment at temperatures from200℃to250℃for12h up to120h. The oxygen-functionalized CNTs were used as starting material for nitrogen functionalization through thermal treatment under NH3. The BET surface area increased after the treatment in HNO3vapor, which also caused the weight loss due to carbon corrosion. The oxygen content and the surface acidity increased with increasing treatment time, but decreased with increasing temperature. As to nitrogen functionalization, the amount of nitrogen was correlated with the oxygen amount in the starting CNTs. A higher NH3concentration resulted in lower BET surface area due to carbon corrosion. The incorporation of both oxygen and nitrogen lowered the thermostability of CNTs.The prepared Pt/CNTs catalysts were evaluated for their performance as catalysts in the hydrogenation of1,5-COD. The reaction is1/2order with respect to H2in the investigated range of1%to6%, and zero order to COD. In the hydrogenation of1,5-COD, it was observed that TOF increases linearly when the Pt particle size increased. However, the TOF of COE remained constant independent of the Pt particle size. Formation of the nitrogen-containing sites with a pyridine-like state should enhance the adhesion between platinum particles and support to stabilizing platinum in a more dispersed state. Pt/NCNTs catalyst due to the higher dispersion of metal displayed higher activity and stability than Pt/oCNTs.Through the use of the same precursors and protocols, Pt-Ru bimetallic nanoparticles with different structures (i.e., core-shell, alloy, and mixtures of monometallic NP) can be prepared selectively. The prepared Pt, Ru, Pt-Ru alloy, Ru@Pt and Pt@Ru nanoparticles fell in the range of1.5-3.0nm in diameter, and were uniformly dispersed on the CNTs. The Pt@Ru/CNTs and Ru@Pt/CNTs core-shell catalysts showed different catalytic properties in selective hydrogenation of phenylacetylene from the Pt-Ru alloy, and the mixed monometallic samples with the correspondingly identical composition.Pt colloids have been synthesized at room temperature through simply introducing acetate to the aged EG solution of H2PtCl6without any other capping agents or surfactants. The amount of acetate added to the reaction solution played a key role in producing Pt colloids and adjusting the size of the Pt nanoparticles. The Pt particle sizes were controlled in the range from2.4to4.2nm by changing the concentration of acetate from2×10-3to3.2×10-1M. The possible formation mechanism is the formation of H2PtCl4(EG)n in the process of aging. During reducing Pt ions by EG, CH3COONa plays the role of catalyst and stabilizing agent. For this reaction pathway to take place, the-OH groups of ethylene glycol interact with Pt-ion sites, resulting in the oxidation of the alcohol groups to aldehydes. These aldehydes are not very stable and can be easily oxidized to glycolic. |
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