Showing papers in "Catalysis Letters in 2004"
TL;DR: An oxide photocatalyst Bi2WO6 with corner-shared WO6 octahedral layered structure was synthesized and its band gap was determined to be 2.69 eV from UV-vis diffuse reflectance spectra as discussed by the authors.
Abstract: An oxide photocatalyst Bi2WO6 with corner-shared WO6 octahedral layered structure was synthesized. Its band gap was determined to be 2.69 eV from UV–vis diffuse reflectance spectra. The photocatalyst showed not only the activity for photocatalytic O2 evolution with the initial evolution rate of 2.0 μmol/h but also the activity of mineralizing both CHCl3 and CH3CHO contaminants under visible light irradiation. Meanwhile, wavelength dependence of CH3CHO decomposition was observed, which indicated that the photocatalytic activity of the photocatalyst was in good agreement with its light-absorption ability.
492 citations
TL;DR: In this article, a self-consistent, periodic density functional theory (DFT) calculations and micro-kinetic modeling are used to compare selectivity for the preferential oxidation of CO (PROX) with respect to H2 based on studies of elementary reaction steps on the (111) facet of Au, Cu and Pt.
Abstract: Self-consistent, periodic density functional theory (DFT) calculations and micro-kinetic modeling are used to compare selectivity for the preferential oxidation of CO (PROX) with respect to H2 based on studies of elementary reaction steps on the (111) facet of Au, Cu and Pt The first step of H oxidation (OH formation) has a higher activation barrier than the second step (H2O formation) on all three metal surfaces, indicating that OH formation competes with CO oxidation for the removal of trace amounts of CO from a typical reformate gas The activation energy barrier for CO oxidation is found to be 018eV on Au(111), 082eV on Cu(111) and 096eV on Pt(111), whereas the barrier for OH formation is 090, 128 and 083eV respectively A micro-kinetic model based on the DFT results shows that trends in the selectivity of these metals at different temperatures is due to (i) differences in the rate constants of the competitive CO and H oxidation reactions, and (ii) differences in the CO and H surface coverages Our results explain why Au and Cu are more selective PROX catalysts compared to Pt at low temperatures At higher temperatures, Pt and Cu lose some of their selectivity to CO oxidation, whereas the selectivity on Au decreases substantially primarily because of the significantly weaker CO adsorption
238 citations
TL;DR: In this paper, the authors examine 13 different metallic catalysts from numerous places within the Periodic Table, and show that the activity varies in the order Ru>Ni>Rh>Co>Ir>Fe≫Pt>Cr>Pd>Cu≫Te, Se, Pb.
Abstract: The catalytic decomposition of ammonia has recently been proposed as a possible source of hydrogen for fuel cells. However, the ruthenium catalyst is costly. Although there exist several correlations for catalytic activity that suggest potentially useful alternatives, the particular candidates differ. The present work seeks to determine experimentally which, if any, of these correlations correctly predicts suitable substitutes. The experiments examine 13 different metallic catalysts from numerous places within the Periodic Table, and show that the activity varies in the order Ru>Ni>Rh>Co>Ir>Fe≫Pt>Cr>Pd>Cu≫Te, Se, Pb. The results suggest that nitrogen desorption limits the rate on Fe, Co, and Ni, whereas N–H bond scission limits the rate on other metals such as Rh, Ir, Pd, Pt, and Cu. Conventional single-parameter correlations of activity generally fail to predict the results because the rate-determining step changes across the data set.
236 citations
TL;DR: In this paper, the absorption edge of rutile titanium dioxide powder was largely shifted from 400 to 700 nm by doping C4+ and S4+ ions into a TiO2 lattice.
Abstract: C4+ and S4+-codoped titanium dioxide (TiO2) having a rutile phase was prepared. By doping C4+ and S4+ ions into a TiO2 lattice, the absorption edge of rutile TiO2 powder was largely shifted from 400 to 700 nm. 2-Methylpyridine and methyleneblue were photocatalytically oxidized at high efficiency on C4+ and S4+-doped TiO2 under visible light at a wavelength longer than 5 nm.
154 citations
146 citations
TL;DR: In this paper, a series of TiO2-ZrO2 mixed oxides with varying molar ratio of Ti2 to ZrO 2 were prepared by the co-precipitation method.
Abstract: A series of TiO2–ZrO2 mixed oxides with varying molar ratio of TiO2 to ZrO2 were prepared by the co-precipitation method. The crystalline phases of the oxides were characterized by XRD and their acid–base properties by TPD of NH3 and CO2 and IR of adsorbed pyridine. The catalytic activities were investigated for the vapor phase dehydration of methanol to dimethyl ether (DME) in a fixed-bed reactor under atmospheric pressure. The mixed oxides are highly amorphous in nature. The acid–base properties and CH3OH conversion activity are increasing with TiO2 content and an optimum value is achieved for a molar ratio of Ti/Zr in the vicinity of 1/1. At lower reaction temperature (<300 °C), the selectivity for DME is nearly 100%. A good correlation is observed between dehydration activity and the acid–base properties of the TiO2–ZrO2 catalysts. It is significant to note that TiO2–ZrO2 catalysts show high stability against water during dehydration reaction. Based on our results, a surface mechanism involving both acid–base sites has been proposed for DME formation.
135 citations
TL;DR: Au catalysts supported on mesoporous silica and titania supports were synthesized and tested for the oxidation of CO as discussed by the authors, and the results suggest that the presence of 2-3 nm particle size alone alone is not sufficient to achieve high activity in CO oxidation.
Abstract: Au catalysts supported on mesoporous silica and titania supports were synthesized and tested for the oxidation of CO. Two approaches were used to prepare the silica-supported catalysts utilizing complexing triamine ligands which resulted in mesoporous silica with wormhole and hexagonal structures. The use of triamine ligands is the key for the formation of uniformly sized 2–3 nm Au nanoparticles in the silica pores. On mesoporous titania, high gold dispersions were obtained without the need of a functional ligand. Au supported on titania exhibited a much higher activity for CO oxidation, even though the Au particle sizes were essentially identical on the titania and the wormhole silica supports. The results suggest that the presence of 2–3 nm particle size alone is not sufficient to achieve high activity in CO oxidation. Instead, the support may influence the activity through other possible ways including stabilization of active sub-nanometer particles, formation of active oxygen-containing reactant intermediates (such as hydroxyls or O2−), or stabilization of optimal Au structures.
134 citations
TL;DR: In this article, a liquid-phase highly efficient selective selective oxidation cyclohexane to cycloencoder and cycloenanone over the Au/MCM-41 catalyst was carried out in a solvent-free system, which oxygen as the only oxidant and the reaction conditions are very moderate.
Abstract: The liquid-phase highly efficient selective oxidation cyclohexane to cyclohexanol and cyclohexanone over Au/MCM-41 catalyst was carried out in a solvent-free system, which oxygen as the only oxidant and the reaction conditions are very moderate. The Au/MCM-41 was characterized by XRD, N2adsorption/desorption, UV-Vis, XPS, and ICP-AES.
121 citations
TL;DR: In this article, new preparation routes were applied to synthesize novel Cu/ZnO catalysts exhibiting high catalytic activity in methanol synthesis, in particular, the deposition-precipitation of copper onto high specific surface area (SSA) zinc oxide particles and the chemical vapor deposition of diethyl zinc.
Abstract: New preparation routes are applied to synthesize novel Cu/ZnO catalysts exhibiting high catalytic activity in methanol synthesis. In particular, the deposition–precipitation of copper onto high specific surface area (SSA) zinc oxide particles and the chemical vapor deposition of diethyl zinc turned out to be effective techniques, leading to promising methanol synthesis catalysts due to the enlargement of the Cu-ZnO interface.
120 citations
TL;DR: In this article, the degradation in aqueous solution of 4-chlorophenol photocatalyzed by band-gap-irradiated TiO2 modified with nanoscopic gold particles was studied as a function of Au particle size by means of HREM, DRIFTS, BET, and reactor measurements.
Abstract: The degradation in aqueous solution of 4-chlorophenol photocatalyzed by band-gap-irradiated TiO2 modified with nanoscopic gold particles has been studied as a function of Au particle size by means of HREM, DRIFTS, BET, and reactor measurements. 4-chlorocatechol is observed as a reaction intermediate, and the results indicate that gold particle size is an important parameter. At low metal loadings, very small Au particles (<3 nm diameter) are particularly effective in enhancing the pseudo first-order rate constant. Higher Au loadings result in much larger particles and a loss of catalytic efficiency. These findings are discussed in terms of possible effects on the rate of production and recombination of photogenerated electrons and holes. It is shown that elimination of adsorbed hydroxyl groups that act as effective hole traps has a deleterious effect on the catalytic efficiency.
119 citations
TL;DR: The mesoporous zeolite single catalysts were generally found to exhibit high activity in these model reactions as discussed by the authors, attributed to the resulting improvements in the mass transport to and from the active sites.
Abstract: New mesoporous silicalite-2, ZSM-11, and titanosilicalite-2 zeolite single crystals were synthesized by use of carbon particles as a mesopore template. After removal of the carbon particles by combustion, zeolite single crystals with intracrystalline mesopore volumes between 0.31 and 0.44 cm3/g were isolated. All samples were characterized by XRD, SEM and adsorption measurements. Isomerization and cracking of n-hexadecane, and epoxidation of oct-1-ene and styrene were chosen as model test reactions. The mesoporous zeolite single catalysts were generally found to exhibit high activity in these model reactions. The advantage of introducing an intracrystalline mesopore system into zeolite catalysts is attributed to the resulting improvements in the mass transport to and from the active sites. This is particularly important for more bulky reactants, intermediates and products and especially under experimental conditions giving high reaction rates.
TL;DR: Magnesia-carbon nanotubes (abbreviated as MgO-CNTs) were prepared by impregnation of CNTs with Mg(NO3)2·6H2O in ethanol solution, followed by drying at 353 K and calcination at 873 K, respectively.
Abstract: Magnesia–carbon nanotubes (abbreviated as MgO–CNTs) nanocomposites were prepared by impregnation of CNTs with Mg(NO3)2·6H2O in ethanol solution, followed by drying at 353 K and calcination at 873 K, respectively. The nanocomposites are thermally more stable than CNTs in a H2 flow. The use of the nanocomposites as support yielded more efficient Ru catalysts for the generation of CO
x
-free hydrogen from NH3 decomposition.
TL;DR: In this paper, a simple decantation procedure without loss of activity was proposed to reuse polyvinyl-2-pyrrolidone (PVP) catalysts.
Abstract: Platinum, palladium and rhodium nanoparticles stabilized by poly(N-vinyl-2-pyrrolidone) (PVP) can be synthesized by ethanolic reduction of the corresponding metal halide salts and when immobilized in an ionic liquid, 1-n-butyl-3-methylimidazolium hexafluorophosphate ([BMI][PF6]), are very effective olefin hydrogenation catalysts which are capable of being recycled by a simple decantation procedure without loss of activity.
TL;DR: Pd/ZnO catalyst exhibits high activity and selectivity for methanol synthesis in the hydrogenation of CO2 under atmospheric pressure PdZn alloys are formed upon reduction of the Pd-Zn O catalyst at high temperatures as mentioned in this paper.
Abstract: Pd/ZnO catalyst exhibits high activity and selectivity for methanol synthesis in the hydrogenation of CO2 under atmospheric pressure PdZn alloys are formed upon reduction of the Pd/ZnO catalyst at high temperatures The catalytic activity and selectivity are greatly enhanced upon the formation of such PdZn alloys The turnover frequency and selectivity of methanol formation are markedly larger than those of a Cu/ZnO type control catalyst
TL;DR: In this paper, the catalytic properties of a CuO/ZrO2 catalyst (8.5wt%) synthesised by a templating technique were investigated with respect to activity, long term stability, CO formation, and response to oxygen addition to the feed.
Abstract: Steam reforming of methanol for production of hydrogen can be carried out over copper based catalyst. In the work presented here, the catalytic properties of a CuO/ZrO2 catalyst (8.5wt%) synthesised by a templating technique were investigated with respect to activity, long term stability, CO formation, and response to oxygen addition to the feed. The results were obtained using a fixed bed reactor and compared to a commercial methanol synthesis catalyst CuO/ZnO/Al2O3. It is shown that, depending on the time on stream, the temporary addition of oxygen to the feed has a beneficial effect on the activity of the CuO/ZrO2 catalyst. After activation, the CuO/ZrO2 catalyst is found to be more active (per copper mass) than the CuO/ZnO/Al2O3 system, more stable during time on stream (measured up to 250h), and to produce less CO. Structural characterisation by means of X-ray powder diffraction (XRD) and X-ray absorption spectroscopy (XAS) reveals that the catalyst (as prepared) consists of crystalline, tetragonal zirconia with small domain sizes (about 60A) and small/disordered crystallites of CuO.
TL;DR: In this paper, the formation of Pd carbide during the synthesis of vinyl acetate (VA) was investigated over Pd/SiO2 catalysts with two different Pd particle sizes.
Abstract: The formation of Pd carbide (PdC
x
) during the synthesis of vinyl acetate (VA) was investigated over Pd/SiO2 catalysts with two different Pd particle sizes, as well as over a Pd–Au/SiO2 mixed-metal catalyst. XRD data show that PdC
x
was produced in the pure Pd catalysts after reaction based on the downshift of the Pd(111) and (200) XRD features. The smaller Pd particles showed greater resistance to the formation of PdC
x
. The XRD and XPS data are consistent with formation of a PdC
x
species at the surface of the Pd–Au catalyst, however, the primary contributor to the downshift of the Pd(111) feature subsequent to reaction in the mixed-metal catalyst is believed to arise from reaction-induced alloying of Au with Pd. The alloying of Au with Pd is apparently very effective in preventing PdC
x
formation in Pd-based catalysts for VA synthesis.
TL;DR: In this article, the conduction bands of the materials are thought to be composed of the W5d orbital hybridized with the Nb5d or Ta4d orbital.
Abstract: Defect pyrochlore-type oxides, AMWO6 (A = Rb, Cs; M = Nb, Ta), loaded with nickel oxide showed photocatalytic activity for overall water splitting under ultraviolet-light irradiation. The conduction bands of the materials are thought to be composed of the W5d orbital hybridized with the Nb5d or Ta4d orbital.
TL;DR: High surface area zirconium phosphate in an amorphous phase exhibits high activities for water-related reactions such as hydrolysis of ethyl acetate and esterification of acetic acid with ethanol as discussed by the authors.
Abstract: High surface area zirconium phosphate in an amorphous phase exhibits high activities for water-related reactions such as hydrolysis of ethyl acetate and esterification of acetic acid with ethanol The zirconium phosphate is insoluble during the reaction, is recoverable by simple filtration, and can be reused at least five times without any treatment
TL;DR: In this article, a quantitative method based on H/D exchange between H2O/D2O molecules and the OH groups of different zeolites has been developed for the titration of the Bronsted acid sites present on the solid surface.
Abstract: An original quantitative method based on H/D exchange between H2O/D2O molecules and the OH groups of different zeolites has been developed for the titration of the Bronsted acid sites present on the solid surface. The measured Bronsted acid sites density appears to be in good agreement with the theoretical amount estimated by the Si/Al ratio. In contrary to classical methods, this non-destructive anhydride method titrates the whole quantity of Bronsted acid sites of zeolites.
TL;DR: In this paper, an alternative commercial LTS (Cu-Zn/Al2O3) catalyst for an onboard gasoline fuel processor was proposed. But, it was found that the Mo2C catalyst showed higher activity and stability than the commercial lTS catalyst, even though both catalysts were deactivated during the thermal cycling runs.
Abstract: Molybdenum carbide catalysts for water–gas shift (WGS) reaction were investigated to develop an alternate commercial LTS (Cu-Zn/Al2O3) catalyst for an onboard gasoline fuel processor. The catalysts were prepared by a temperature-programmed method and were characterized by N2 physisorption, CO chemisorption, XRD and XPS. It was found that the Mo2C catalyst showed higher activity and stability than the commercial LTS catalyst, even though both catalysts were deactivated during the thermal cycling runs. The optimum carburization temperature for preparing Mo2C was in the range of 640–650 °C. It was found that the deactivation of the Mo2C catalyst was caused by the transition of Moδ+ (IV < δ+ < VI, MoOxCy), MoIV and Mo2C on the surface of the Mo2C catalyst to MoVI (MoO3) with the reaction of H2O in the reactant. It was identified that molybdenum carbide catalyst is an attractive candidate for the alternate Cu-Zn/Al2O3 catalyst for automotive applications.
TL;DR: Using n-octane containing thiophene as the model compound, the authors in this article studied the reactivity of thiophenic sulfur compound in gasoline, which is a key step for the oxidative deep desulfurization of gasoline.
Abstract: Thiophene is a typical thiophenic sulfur compound in gasoline. Using n-octane containing thiophene as the model compound, the oxidation of thiophene, which is a key step for the oxidative deep desulfurization of gasoline, was carried out to study the reactivity of thiophene in oxidation reactions. It has been observed that thiophene oxidation can occur using water or t-butanol as solvent. Kinetics of the reaction shows a pseudo-first-order toward thiophene or catalyst and a zero order toward hydrogen peroxide. The mechanism for this unique reaction was proposed as the activation of conjugated electron in thiophene ring.
TL;DR: In this article, the reactions of the heptamethylbenzenium cation in a H-beta zeolite was studied at 300 °C by feeding its corresponding base (WHSV = 0.4 h−1).
Abstract: Recent studies have pointed to the heptamethylbenzenium cation as a prominent intermediate in the methanol to hydrocarbons (MTH) reaction. The reactions of the heptamethylbenzenium cation in a H-beta zeolite was studied at 300 °C by feeding its corresponding base (WHSV = 0.4 h−1). The reactant was converted completely into aliphatic products, polymethylbenzenes and coke under the employed conditions. The results testify that the proposed reaction intermediate yields the same product spectrum as methanol. The composition of the material retained in the catalyst micropores after 15 min of reaction was determined by dissolving the catalyst in 15% HF. Polymethylated benzenes (predominantly pentamethylbenzene), dihydro-trimethylnaphthalenes, and hexamethylnaphthalene were the major components. The results also support the idea that the lowest naphthalene derivative is formed from the heptamethylbenzenium cation by a molecular rearrangement. Hence, the heptamethylbenzenium cation is inherently linked to both product formation and catalyst deactivation in the MTH reaction.
TL;DR: In this paper, the performance of Pd supported on two polymers of similar basicity but different electrical properties, a π-conjugated conducting-polypyrrole (PPY) and the electro-inactive poly(4-vinylpyridine) (PVP) have been studied in the hydrogenation of acetophenone (ACT) and compared with that of γ-Al2O3 supported Pd.
Abstract: Catalytic properties of Pd supported on two polymers of similar basicity but different electrical properties, a π-conjugated conducting-polypyrrole (PPY) and the electro-inactive poly(4-vinylpyridine) (PVP) have been studied in the hydrogenation of acetophenone (ACT) and compared with that of γ-Al2O3 supported Pd. Experimental evidences provided by several techniques: X-ray photoelectron spectroscopy (XPS), scanning (SEM) and transmission electron (TEM) microscopy, X-ray diffraction (XRD) and temperature programmed desorption (TPD) of hydrogen show that both polymers PVP and PPY exhibited ability to stabilize finely dispersed palladium nanoparticles, better this ability is offered by electro-inactive PVP. Palladium nanoparticles within a narrow range of size 2–20nm as well as very high surface concentration of Pd (22.2at %) in agglomerates were established in the latter polymer supported catalysts. Distinctly lower surface concentration of Pd (1.8at %) and crystalline Pd particles of dimension within a wide range, from 5nm up to ca. 1500nm appeared in the matrix of electroactive polymer – PPY. The hydrogenation of ACT to ethylbenzene (ETB) via 1-phenylethanol (ACP) (as the intermediate) proceeded over all studied catalysts. The effects of solvents, Pd content, ACT concentration and the additives of ACP, ETB were also studied. The catalytic properties of Pd/PPY in terms of activity and selectivity significantly differ from those of Pd/PVP and Pd/Al2O3. Both latter catalysts offered high activity and selectivity in the C=O in ACT to C–OH reduction. Definitely lower activity and higher tendency towards the hydrogenolysis of C–OH in ACP reflected Pd/PPY catalysts. Such unprofitable properties of Pd/PPY can be attributed to relatively strong adsorption of all organic reactant ACT, ACP, ETB. A competition of the ACP and ETB with the ACT occurred only in the case of Pdcentres created in the electroactive polymer, whereas Pd sites dispersed in the electro-inactive PVP similarly as the ones in Al2O3 exhibited definitely more substrate – ACT specific character.
TL;DR: In this paper, the marginal activity of 1 wt% Ag impregnated on γ-Al2O3 or mesoporous Al 2O3 modifications is boosted to nearly 100% over a broad temperature range from 200 to 550°C at a space velocity of 30,000cm3g−1h−1).
Abstract: Addition of H2 to a NO/NH3/O2/H2O feed for selective catalytic reduction of nitrogen oxide over Ag/Al2O3 catalysts causes an unusual enhancement of activity, e.g., the marginal activity (<10%) of 1 wt% Ag impregnated on γ-Al2O3 or mesoporous Al2O3 modifications is boosted to nearly 100% over a broad temperature range from 200 to 550°C at a space velocity of 30,000cm3g−1h−1). Contrary, silver on SiO2 or α-Al2O3 shows no improvement of activity in the presence of H2. The effect is tentatively attributed to a higher percentage of intermediary nano-sized Ag clusters on high-surface area Al2O3 in the presence of hydrogen. This promotes oxygen activation and hence NO oxidation to reactive intermediate nitrite species. The required dispersion of Ag cannot be stabilized on SiO2 or α-Al2O3.
TL;DR: In this paper, the transformation of olefin to aromatics over ZSM-5 catalysts with different K-loadings has been investigated both in a continuous flow fixed-bed reactor and in a pulse microreactor.
Abstract: The transformation of olefin to aromatics over ZSM-5 catalysts with different K-loadings has been investigated both in a continuous flow fixed-bed reactor and in a pulse microreactor Investigation of variation of olefin aromatization activity with K-loadings shows that strong acid sites are indispensable for the converting of olefin to aromatics As intermediates of olefin aromatization process, butadiene and cyclopentene not only show much higher aromatization activity than mono-olefins, but also can be transformed into aromatics over relatively weak acid sites of K/ZSM-5 A proposal is put forward, stating that among all the steps experienced in olefins aromatization, the formation of diene or cycloolefin from mono-olefins through hydrogen transfer is the key step and can be catalyzed by strong acid sites
TL;DR: In this paper, the authors used Co2-ZrO2 solid solution catalysts for the selective synthesis of propylene carbonate (PC) from propylene glycol and carbon dioxide.
Abstract: CeO2–ZrO2 solid solution catalysts are very effective for the selective synthesis of propylene carbonate (PC) from propylene glycol and carbon dioxide. Dipropylene glycols and poly (PC) are expected to be formed as by-products, however, they were not detected at all in the analysis by gas chromatograph and FTIR.
TL;DR: In this article, a detailed microkinetic model for NH3 decomposition on Ru using the unity bond index-quadratic exponential potential (UBI-QEP) method was proposed.
Abstract: N–N adsorbate–adsorbate interactions on a Ru(0001) surface are first estimated using quantum mechanical density functional theory (DFT) calculations, and subsequently incorporated, for the first time, in a detailed microkinetic model for NH3 decomposition on Ru using the unity bond index-quadratic exponential potential (UBI–QEP) method. DFT simulations indicate that the cross N–H interactions are relatively small. Microkinetic model predictions are compared to ultra-high vacuum temperature programmed desorption and atmospheric fixed bed reactor data. The microkinetic model with N–N interactions captures the experimental features quantitatively. It is shown that the N–N interactions significantly alter the rate determining step, the most abundant reaction intermediate, and the maximum N*-coverage, compared to mechanisms that ignore adsorbate–adsorbate interactions.
TL;DR: In this paper, the ability to produce H2, the liquid phase product distribution and the catlyst stability of these promoted nano catalysts all depended on the Pt loading and catalyst preparation procedure.
Abstract: TiO2 nanotubes promoted with Pt metal were prepared and tested to be the photocatalytic dehydrogenation catalyst in neat ethanol for producing H2 gas (C2H5OH→→→C3CHO +H2). It was found that the ability to produce H2, the liquid phase product distribution and the catlyst stability of these promoted nano catalysts all depended on the Pt loading and catalyst preparation procedure. These Pt/TiO2 catalysts with TiO2 nanotubes washed with diluted H2SO4 solution produced 1, 2-diethoxy ethane (acetal) as the major liquid phase product, while over those washed with diluted HCl solution or H2O, acetaldehyde was the major liquid phase product.
TL;DR: In this paper, zero valent platinum nanoparticles were stabilized in solution by the use of poly(amido)amine dendrimers and were subsequently deposited onto a porous silica support.
Abstract: Zero valent platinum nanoparticles were stabilized in solution by the use of poly(amido)amine dendrimers and were subsequently deposited onto a porous silica support. The resulting materials were subjected to various thermal treatments in oxidizing, reducing, and inert environments, in order to remove the surrounding polymer and expose the Pt metal sites to gas phase reagents. The materials were characterized at several different stages during this process via Fourier-Transform Infrared (FTIR) spectroscopy and Transmission Electron Microscopy (TEM). The results suggest that the dendrimer decomposition occurs at its mono-substituted amide groups and begins at relatively low temperatures (∼50 °C). The presence of oxygen in the gas phase and the Pt particles in the Pt-dendrimer nanocomposite accelerate this process. Oxidation at 425 °C was the most successful temperature for removing the dendrimer fragments from the Pt surface, rendering the Pt sites most accessible for carbon monoxide adsorption. Limited sintering of the Pt particles is observed under these conditions, as well as during subsequent reduction steps, necessary to yield the metallic form of Pt.
TL;DR: Co-support compound formation (Co-SCF) in Co/TiO2 was found during standard reduction resulting in a lower reducibility of the catalyst and the compound formed is considered to be non-reducible at temperatures <800°C during TPR and different from CoTiO3 as mentioned in this paper.
Abstract: Co-support compound formation (Co-SCF) in Co/TiO2 was found during standard reduction resulting in a lower reducibility of the catalyst. The compound formed is considered to be non-reducible at temperatures <800°C during TPR and different from CoTiO3. The characteristics of Co-SCF were investigated using BET surface area, XRD, Raman spectroscopy, SEM/EDX, and TPR.