Anita Horváth

Hydrogenation of acetylene over low loaded Pd and Pd-Au/SiO2 catalysts

Abstract Acetylene hydrogenation and formation of surface deposits have been investigated on two series of Pd and Pd-Au/SiO2 catalysts differing in metal particle size (D=0.47 and 0.08). Gold was deposited via ionization of pre-adsorbed hydrogen over pre-reduced Pd/SiO2 in order to ensure selective poisoning of the Pd surface. The non-steady-state regime of operation and the accumulation of hydrocarbonaceous overlayer were tested in pulse-flow experiments. Concentration of surface hydrocarbonaceous deposits accumulated during different treatments was also determined by temperature programmed oxidation (TPO). Hydrocarbon overlayer was observed to form immediately and its presence appeared to be a necessary requisite to get steady-state conversion and selectivity data. A large excess of hydrogen suppressed the formation of carbonaceous laydown and increased the over-hydrogenation of acetylene. Presence of Au decreased the carbon coverage and improved the ethene selectivity. Decoration of Pd by Au and the morphology of particles explain the ethene selectivity improvement.

Silica-supported Au nanoparticles decorated by TiO2 : Formation, morphology, and CO oxidation activity

Au-TiO(2) interface on silica support was aimed to be produced in a controlled way by use of Au hydrosol. In method A, the Au colloids were modified by hydrolysis of the water-soluble Ti(IV) bis(ammoniumlactato)dihydroxide (TALH) precursor and then adsorbed on Aerosil SiO(2) surface. In method B, Au sol was first deposited onto the SiO(2) surface and then TALH was adsorbed on it. Regular and high-resolution transmission electron microscopy (TEM and HRTEM) and energy dispersive spectrometry (EDS) analysis allowed us to conclude that, in method A, gold particles were able to retain the precursor of TiO(2) at 1.5 wt % TiO(2) loading, but at 4 wt % TiO(2) content the promoter oxide appeared over the silica surface as well. With method B, titania was detected on silica at each TiO(2) concentration. In Au-TiO(2)/SiO(2) samples, the stability of Au particles against sintering was much higher than in Au/TiO(2). The formation of an active Au-TiO(2) perimeter was proven by the greatly increased CO oxidation activity compared to that of the reference Au/SiO(2).

Pd nanoparticles prepared by "controlled colloidal synthesis" in solid/liquid interfacial layer on silica. I. Particle size regulation by reduction time

Controlled colloidal synthesis (CCS) was developed to prepare monodisperse palladium particles in the nano-scale range on suspended SiO2 particles in an ethanol–toluene mixture. On colloidal SiO2 an about 1 nm thick ethanol-rich adsorption layer was produced in adsorption equilibrium with the liquid mixture. Ethanol served as a reducing agent for the Pd(II) ions diffusing from a toluene-rich liquid solution into the interfacial layer. The low reduction rate ensures the dominancy of particle growth over the nucleation of palladium during the reduction process after the initial nucleation. The relation between the reduction time and the particle size produced was studied. XRF, XPS, TEM, CO chemisorption, and benzene hydrogenation as catalytic test were employed to characterize the samples prepared using different reduction time.

From Molecular Clusters to Metal Nanoparticles

Different methods to prepare supported metal nanoparticles of uniform size are discussed. (i) Supported ruthenium particles were generated from Ru and Ru-Fe bimetallic molecular metal carbonyl cluster precursors (MCC). (ii) Gold nanoparticle formation in the supercage of Y zeolite was studied on Au/NaY, Au/HY and Au-Fe/HY system. (iii) Palladium nanoparticles were grown in liquid phase then deposited on an SiO2 support or they were grown on the support surface in a solid-liquid interfacial layer. The particle size control was more efficient in the latter two cases than in the preparation starting from MCC.

Silica-Supported Au Nanoparticles Decorated by CeO2: Formation, Morphology, and CO Oxidation Activity

Silica-Supported Au Nanoparticles Decorated by CeO2: Formation, Morphology, and CO Oxidation Activity Anita Horv ath,* Andrea Beck, Gy€orgyi Stefler, Tímea Benk o, Gy€orgy S afr an, Zsolt Varga, Jen 00 o Gubicza, and L aszl o Guczi Department of Surface Chemistry and Catalysis and Department of Radiation Safety, Institute of Isotopes of HAS, P.O. Box 77, H-1525 Budapest, Hungary Research Institute for Technical Physics and Materials Science of HAS, P.O. Box 49, H-1525 Budapest, Hungary Department of Materials Physics, E€otv€os Lor and University, Budapest, P.O. Box 32, H-1518, Hungary

TPO characterization of ethanol reduced Pd nanoparticles supported on SiO2

Abstract Silica-supported Pd catalysts were prepared at 298–353 K from Pd(II) chloride or Pd(II) acetate in suspension of SiO2 and ethanol-water or ethanol-toluene mixtures, respectively. Reduction of Pd ions diffusing from liquid phase was ensured in an ethanol-rich adsorption layer covering the SiO2 particles. Temperature-programmed oxidation (TPO) measurements were performed to characterize the organic impurities retained by solid phase. Vapour phase reduction/adsorption experiments with ethanol confirmed that under the reported reduction conditions, the Pd nanoparticles decompose ethanol and the CO formed remains chemisorbed on the Pd sites. Upon contacting the samples with air during the drying process to eliminate the solvent, the CO molecules are immediately removed from Pd sites by O2, and thereby, a significant fraction (22–34%) of Pd sites becomes accessible for catalytic reactions.

Sol-derived Pd/SiO2 catalyst: characterization and activity in benzene hydrogenation

Abstract Pd/SiO2 catalysts were prepared by adsorption of Pd sols on support Aerosil 200 and characterized by transmission electron microscopy (TEM), CO chemisorption and temperature programmed oxidation (TPO). The Pd hydrosols were generated from PdCl2 solution and ethanol as reducing agent in the presence of poly(diallyldimethylammonium chloride), PDDA. The pH of the solution was increased to ensure adsorption of the Pd sol with high concentration of PDDA. The catalytic activity was tested in benzene hydrogenation. The presence of organic impurities and the role of morphology affecting the activity have been discussed in terms of the preparation procedure applied.

Effect of different treatments on Aerosil silica-supported Pd nanoparticles produced by ‘controlled colloidal synthesis’

Abstract Pd nanoparticles were prepared by ‘controlled colloidal synthesis’ (CCS) using aerosil silica support. On SiO 2 , 1–2 nm thick ethanol-rich adsorption layer in ethanol–toluene and ethanol–water mixtures was formed into which Pd(II) ions diffused and were reduced there by ethanol. Using Pd(II)-acetate precursor in an ethanol–toluene mixture (sample G1) and PdCl 2 precursor in an ethanol–water mixture (sample G2), palladium particles of 7.0 and 8.8 nm size, respectively, were produced. Effects of treatments in air and hydrogen were studied on the Pd/SiO 2 samples. The Pd particles showed a twofold/threefold increase in the catalytic activity in benzene hydrogenation after treatment in air at 573 K. The activity increase cannot be explained by a change in the particle size as indicated by transmission electron microscopy (TEM) and CO chemisorption data. Augmentation of turnover number is interpreted by the removal of carbonaceous residues and by the restructuring of the surface caused by carbon removal followed by PdO/Pd transition in the subsequent hydrogen treatment.

Facile ring opening of 2,3-epoxy-steroids with aromatic amines in ionic liquids

Efficient ring opening of steroidal 2,3-epoxides with stoichiometric amount of aromatic amines has been carried out using an ionic liquid ([bmim](+)[BF(4)](-)) both as solvent and catalyst. The reactions were completely regio- and stereoselective in each case. The aminoalcohol products have chair conformations in ring A. The ionic liquid-mediated ring opening can efficiently be carried out with aliphatic amines like morpholine as well.

75 Controlling metal particle size in preparation of Pd/SiO2 catalysts

Abstract Palladium nanoparticles have been fabricated on Aerosil 200 support using (i) “Controlled Colloidal Synthesis”, (ii) PDDA stabilized Pd sol (both liquid phase reduction with ethanol) and (iii) incipient wetness method (as reference) Oxidation/reduction treatment was employed to remove the carbonaceous impurities from the samples during which no change in the particle size was experienced. However, the turnover frequency referred to Pd surface exposed significantly changed and FTIR technique was used to monitor the alteration of Pd surface by means of CO chemisorption It turned out that after treatment the distribution of the overlapping stretching band system of the prevailing bridge CO forms was changed indicating either a change in the face orientation of Pd crystallites, or formation of clean Pd faces in oxidation/reduction process