Pârvulescu Vasile I, Pârvulescu Viorica, Endruschat Uwe, Granger Pascal, Richards Ryan
University of Bucharest, Faculty of Chemistry, Department of Chemical Technology and Catalysis, B-dul Regina Elisabeta 4-12, Bucharest 030016, Romania.
Chemphyschem. 2007 Apr 2;8(5):666-78. doi: 10.1002/cphc.200600571.
Sol-gel synthesis of silica and silica-tantalum oxide embedded platinum nanoparticles is carried out using Pt colloids as templates. These colloids are prepared by reduction with Na[AlEt(3)H] and stabilized with different ligands (ammonium halide derivatives, non-ionic surfactants with polyether chains, and 2-hydroxy-propionic acid). The aim of the present study is to prepare mesoporous silica embedded Pt colloids combining the "precursor concept" with the model of catalyst preparation using preformed spheres. Nanoparticles of Pt incorporated in high surface area mesoporous materials are formed after calcination. Further, it is observed that calcination of these catalysts causes partial aggregation and oxidation of the parent colloids, a process that is largely dependent on the nature of the stabilizing ligands. Several methods have been used for characterization of these materials: adsorption-desorption isotherms at 77 K, H(2) chemisorption, X-ray diffraction(XRD), (29)Si and (13)C magic angle spinning (MAS) NMR, ammonia diffuse reflectance Fourier transform infrared spectroscopy (NH(3)-DRIFT), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). It is found that both metal oxide systems exhibit Brønsted acidity (weaker for silica and quite strong for silica-tantalum oxide). In addition, NH(3)-DRIFT experiments demonstrate the oxidative properties of the surface. Part of the adsorbed NH(4) (+) species is oxidized to N(2)O. Testing these catalysts in the reduction of NO and NO(2) with isopentane under lean conditions indicate that the activity of these catalysts is indeed dependent on the size of the platinum particles, with those of size 8-10 nm demonstrating the best results. The support likely contributes to this effect, particularly after Ta incorporation into silica.
以铂胶体为模板，通过溶胶 - 凝胶法合成了二氧化硅以及二氧化硅 - 钽氧化物负载的铂纳米颗粒。这些胶体通过用Na[AlEt(3)H]还原制备，并使用不同的配体（卤化铵衍生物、具有聚醚链的非离子表面活性剂和2 - 羟基丙酸）进行稳定化处理。本研究的目的是将“前驱体概念”与使用预制球体的催化剂制备模型相结合，制备介孔二氧化硅负载的铂胶体。煅烧后形成了负载在高比表面积介孔材料中的铂纳米颗粒。此外，观察到这些催化剂的煅烧会导致母体胶体的部分聚集和氧化，这一过程在很大程度上取决于稳定配体的性质。已经使用了几种方法来表征这些材料：77 K下的吸附 - 脱附等温线、H(2)化学吸附、X射线衍射（XRD）、(29)Si和(13)C魔角旋转（MAS）核磁共振、氨漫反射傅里叶变换红外光谱（NH(3)-DRIFT）、透射电子显微镜（TEM）和X射线光电子能谱（XPS）。发现两种金属氧化物体系均表现出布朗斯台德酸性（二氧化硅较弱，二氧化硅 - 钽氧化物较强）。此外，NH(3)-DRIFT实验证明了表面的氧化性质。部分吸附的NH(4)(+)物种被氧化为N(2)O。在贫氧条件下用异戊烷还原NO和NO(2)对这些催化剂进行测试表明，这些催化剂的活性确实取决于铂颗粒的尺寸，尺寸为8 - 10 nm的颗粒表现出最佳结果。载体可能对此效应有贡献，特别是在将钽掺入二氧化硅之后。
