Tarek M. Salama

Studies of the selective reduction of nitric oxide by carbon monoxide in the presence and absence of hydrogen over Au/NaY catalysts

The selective reduction of NO with CO in the presence and absence of hydrogen over Au/NaY catalysts has been studied by in situ FTIR spectroscopy and under steady-state conditions in a flow mode in the temperature range 473–723 K. The NCO intermediates found by FTIR absorption at 2280–2240 cm–1 after contacting, at 423–573 K, an Au/NaY catalyst with an NO–CO–H2 mixture shows a dependence on the presence of H2 which functions in N—O dissociation in this temperature region. Removal of NCO groups from the catalyst with time at 473 K, proposed to be limited by the prerequisite reaction between adsorbed NCO and NO in the gas phase, to form N2 and CO2 is accelerated with increasing temperatures. The effect of adding H2 to an NO–CO–He stream on the conversions of both NO and CO to, respectively, N2 and CO2 were found to be consistent with a temperature-dependent mechanism. The yields of N2 and CO2 were increased in the presence of hydrogen, when NCO complexes were present on the gold catalyst, up to 573 K. Above this temperature, where direct NO + CO is the only competing reaction, the presence of hydrogen reduced conversion. The activities of the gold catalysts were maintained even at temperatures as high as 723 K, suggesting that a large fraction of partially charged AuI cations were stabilized by the framework of NaY zeolite. This species, after pumping off the reacting mixture gases at 473 K and collecting the spectra on cooling the gold catalyst, gave a characteristic carbonyl IR absorption band at 2188 cm–1, reasonably assigned to a CO vibration of carbonyl coordinated to AuI.

X-ray absorption spectroscopic and electron paramagnetic resonance studies on the strong metal–support interaction of platinum supported on titania dispersed on silica

The hydrogen-treated (at 623 and 773 K) Pt/TiO2–SiO2 catalyst was characterized by using Pt L-edge X-ray absorption near-edge structure (XANES), extended X-ray absorption fine structure (EXAFS), and electron paramagnetic resonance (EPR) spectroscopies to elucidate the role of the dispersed TiO2 in establishing the strong metal–support interaction (SMSI) state of the platinum.The dispersed TiO2 decreased the height of the XANES peak at 15 eV above the absorption edge, the coordination number of the Pt–Pt shell and the Pt–Pt interatomic distance relative to the corresponding Pt foil and Pt/SiO2 data. These observations are interpreted by the decrease in Pt particle size (intrinsic effect) in the presence of the dispersed TiO2 since no shell other than the Pt–Pt shell was detectable in the Fourier transforms of k3-weighted EXAFS. Raising the H2 treatment temperature from 623 to 773 K did not cause significant changes in the XANES/EXAFS features.Two signals at g= 2.03 (due to Pt+) and g= 1.905 (due to Ti3+) were observed on EPR measurement (at 77 K) of the hydrogen-treated and evacuated Pt/TiO2–SiO2. The intensities of both signals increased on raising the H2 treatment temperature from 623 to 773 K. These ions (Pt+ and Ti3+) are formed by electron transfer from a Pt atom to a Ti4+ ion at the metal/support interface rather than by reverse spillover of spilt-over hydrogen species. This kind of interaction is typical of the dispersed TiO2 and is suggested to play a significant role in the generation of the SMSI state of the Pt/TiO2–SiO2 catalyst.

Surface properties of ZrO2 dispersed on SiO2

Zirconium oxide microcrystals were dispersed on SiO2 from methanol or toluene solution of corresponding zirconium compounds and the surface properties in terms of the acid-base concept was examined by means of a temperature-programmed-desorption technique. Though bulk zirconium dioxide exhibited both acidic and basic properties, surface zirconium oxide lost the basic properties.

EXAFS/XANES study of titanium oxide supported on SiO2: a structural consideration on the amorphous state

Titanium oxide microcrystals were dispersed on SiO2 from a toluene solution of the corresponding alkoxide and the structure of the thus prepared oxide was examined by means of extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES). Though the dispersed oxide is in the amorphous state, analysis of EXAFS/XANES revealed that an anatase-like local structure of TiOx was formed on the SiO2 surface selectively.

Effect of titania over silica as support for platinum catalyst on butane hydrogenolysis

The group VIII metals/TiO[sub 2] systems have received attention in strong metal-support interaction (SMSI) because of its promising potential in controlling the catalytic performance (activity and selectivity) of the supported metal catalysts. Concerning the support, it has been reported that the SMSI behavior strongly depends on the nature and/or environment of the TiO[sub 2]. The nature of the dispersed TiO[sub 2] on other metal oxides should be different from that of bulk TiO[sub 2]. Thus, the metal-support interaction between dispersed TiO[sub 2] and the Pt particle can be expected to be different from that occurring on bulk TiO[sub 2]. In this note, the authors report the evidences for the metal-support interaction between dispersed TiO[sub 2] phase on SiO[sub 2] and supported Pt particles by the combined TPR-TPD technique and butane hydrogenolysis. The two types of the metal-support interactions (light SMSI and deep SMSI) playing different roles in H[sub 2] adsorptivity and hydrogenolysis activity of platinum particles are proposed.

Low-temperature catalytic decomposition of NO over excess-loading gold(I) in NaY zeolite

The intrazeolite Aul in NaY zeolite exhibits remarkable catalytic activities in the decomposition of NO to N2(N2O) and O2 at low temperatures; the NO decomposition reaction proceeds through the sequential formation of N2O3 and N2O intermediates on Aul/NaY at 300–673 K.

In situ FT-IR and catalytic studies of the selective reduction of nitric oxide by carbon monoxide over Au/NaY catalysts: Effect of adding hydrogen to the reaction gas mixture

Abstract The role of hydrogen in the selective reduction of NO by CO over Au/NaY catalysts has been discussed. The NCO intermediates detected by FT-IR absorption at 423–573 K shows a dependence on the presence of H 2 which functions in N-O dissociation. The yields of N 2 and CO 2 were increased in the presence of hydrogen when NCO complexes were present in the gold catalyst up to 573 K. Above this temperature, where direct NO+CO is the only competing reaction, the presence of hydrogen reduced conversions. The results indicated that dual Au I and Au O sites are effective in maintaining higher activities of gold catalysts for the above reaction. The Au I species gave a characteristic carbonyl IR absorbing band at 2188 cm −1 .

REMARKABLE OXYGEN PROMOTION OF THE SELECTIVE REDUCTION OF NITRIC OXIDE BY HYDROGEN OVER AU/NAY AND AU/ZSM-5 ZEOLITE CATALYSTS

A significant enhancement of the selective reduction of nitrogen oxide nby H n 2 n is produced in the presence of oxygen over Au/NaY and nAu/ZSM-5 catalysts by forming NO n 2 n and N n 2 nO n 4 n nintermediates, which are eventually reduced to N n 2 n.

Preparation of active platinum hydrogenolysis catalyst supported on TiO2 phase dispersed on SiO2

Platinum catalysts supported on a TiO2 phase well-dispersed on SiO2 (TiO2/SiO2) exhibited a high activity for butane hydrogenolysis; activity was 1∼2 orders of magnitude higher than those of platinum catalysts supported on SiO2 and TiO2.AbstractКатализаторы Pt, нанесенные на TiO2, хорошо дисперсированным на фазе SiO2 (TiO2/SiO2), обладают высокои активностью к гидрогенолизу бутана; эта активностя оказалась на 1∼2 порядка выше по сравнению с обычными платиновыми ктализаторами, нанесенными на SiO2 и TiO2.

EXAFS study of thin-film zirconium oxide deposited on a TiO2 surface

Zirconium oxide overlayers have been prepared by deposition of Zr cations on the TiO2 surface from a solution of zirconium butoxide in toluene. The structures of the samples thus prepared were characterized by means of EXAFS. Fourier transforms of the Zr K-edge EXAFS of a sample containing 0.245 g of Zr g–1 TiO2 show that the Zr cation surface species are present in an amorphous state. Curve-fitting analysis for the Zr–O shells indicates that the environment of the deposited zirconium cations is almost the same as that found in monoclinic ZrO2. Although for high Zr samples the ZrO2 exists as a three-dimensional monoclinic phase, as revealed by XRD, the zirconium oxide species in lower deposition samples is dispersed over titania as a two-dimensional overlayer.