Showing papers on "Temperature-programmed reduction published in 2005"
TL;DR: It is suggested that the presence of small gold particles, as obtained by the SMAD technique, is not the main requisite for the achievement of the highest CO conversion, and the strong interaction between ionic gold and ceria, by enhancing the ceria surface oxygen reducibility, may determine the particularly high activity.
Abstract: Gold catalysts supported on cerium oxide were prepared by solvated metal atom dispersion (SMAD), by deposition-precipitation (DP), and by coprecipitation (CP) methods and were characterized by X-ray diffraction (XRD), temperature programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS). The catalytic activity was tested in the CO oxidation reaction. The structural and surface analyses evidenced the presence of a modified ceria phase in the case of the DP sample and the presence of pure ceria and gold metal crystallites in the case of the SMAD and CP samples. The DP sample, after a mild treatment in air at 393 K, exhibited only ionic gold, and it was very active below 273 K. By comparing the activities of the different catalysts, it is suggested that the presence of small gold particles, as obtained by the SMAD technique, is not the main requisite for the achievement of the highest CO conversion. The strong interaction between ionic gold and ceria, by enhancing the ceria surface oxygen reducibility, may determine the particularly high activity.
269 citations
TL;DR: In this article, low-content gold-ceria catalysts were used for the PROX reaction in a realistic fuel gas mixture containing 1% CO −0.5% O 2 −50% H 2 O −10% H2 O −15% CO 2.
Abstract: Low-content ( 2 -TPR, was used to normalize the WGS reaction rates. Cyclic temperature-programmed reduction with intermittent reoxidation showed that the surface structures of gold-ceria catalysts are highly reversible. Considerable reoxidation by oxygen or H 2 O can occur even at ambient conditions. The stability of low-content gold-ceria catalysts for the PROX reaction in a realistic fuel gas mixture containing 1% CO–0.5% O 2 –50% H 2 –10% H 2 O–15% CO 2 –He was excellent. No drop in activity or selectivity was found in cyclic operation up to 150 °C.
220 citations
TL;DR: In this paper, the catalytic performance of gold-supported titania nanotubes (Au/TNTs) was evaluated for the first time in water-gas shift reaction (WGSR) at wide temperature range (140-300 °C) and has been compared with Au/surfactant-templatedmesoporous titania and Au/Al 2 O 3 catalysts under the same operating conditions.
Abstract: Titanium oxide nanotubes (TNTs) have been synthesized via the reaction of TiO 2 crystalline powders of either anatase or rutile phase and NaOH aqueous solution. Their application as an active supports of gold particles prepared by deposition–precipitation (DP) method is investigated. The TNT supports and the gold catalysts were characterized by a range of methods including powder X-ray diffraction (XRD), transmission electron microscopy (TEM), N 2 adsorption analysis and temperature programmed reduction (TPR). The catalytic activity of gold-supported titania nanotubes (Au/TNTs) was evaluated for the first time in water-gas shift reaction (WGSR) at wide temperature range (140–300 °C) and has been compared with Au/surfactant-templated-mesoporous-titania and Au/Al 2 O 3 catalysts under the same operating conditions. We try to establish a correlation between the catalytic performance of Au/TNTs and the nature of the support.
192 citations
TL;DR: In this article, Ni/LaAlO3 and Ni/SrTiO3 showed high catalytic activities among Ni/perovskites and longer-term stabilities than the conventional Ni/α-Al2O3 catalyst.
Abstract: Steam reforming of methane for the purpose of hydrogen production was performed using nickel catalysts supported on a variety of perovskites, including LaAlO3, LaFeO3, SrTiO3, BaTiO3, La0.4Ba0.6Co0.2Fe0.8O3−δ, to compare the catalytic activity and resistance to coking of these catalysts to those of the conventional Ni/α-Al2O3 catalyst. Ni/LaAlO3 and Ni/SrTiO3 showed high catalytic activities among the Ni/perovskites and longer-term stabilities than the conventional catalyst. Temperature programmed oxidation of carbon deposited on used catalysts revealed that inactive carbon species detected on Ni/α-Al2O3 were not formed in the case of Ni/LaAlO3. The results of temperature programmed reduction confirmed that consumption and recovery of the lattice oxygen in perovskites occurred during the reaction, and that the reducibility of perovskites had a great impact on the steam reforming activity. The lattice oxygen in perovskites is considered to play important roles in promoting the oxidation of CHx fragments adsorbed on metallic nickel.
171 citations
TL;DR: A series of copper catalysts supported on TiO2-ZrO2 with copper loading varying from 1.0 to 21.6 wt % were prepared by a wet impregnation method and results suggest that the copper oxide is present in a highly dispersed amorphous state at copper loadings <16.8 wT % and as a crystalline CuO phase at higher Cu loadings.
Abstract: A series of copper catalysts supported on TiO2-ZrO2 with copper loading varying from 1.0 to 21.6 wt % were prepared by a wet impregnation method. The catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy, electron spin resonance (ESR), temperature programmed reduction (TPR), and Brunauer-Emmett-Teller specific surface area measurements. Copper dispersion and metal area were determined by N2O decomposition by the passivation method. XRD results suggest that the copper oxide is present in a highly dispersed amorphous state at copper loadings <16.8 wt % in the sample and as a crystalline CuO phase at higher Cu loadings. Copper dispersion increases with Cu loading up to 5.1 wt % and levels off at higher loadings. The XPS peak intensity ratios of Cu 2p(3/2)/Ti 2p(3/2) and Cu 2p(3/2)/Zr 3d(5/2) were compared with the copper dispersion calculated from N2O decomposition. ESR results suggest the presence of two types of copper species on the TiO2-ZrO2 support. TPR profiles reveal the presence of highly dispersed copper oxide at lower temperatures and bulk CuO at higher temperatures. The catalytic properties were evaluated for the vapor-phase dehydrogenation of cyclohexanol to cyclohexanone and related to the dispersion of Cu on TiO2-ZrO2.
152 citations
TL;DR: Pt/CeO2, Pt/ZrO2 and Pt/CexZr1−xO2 catalysts containing different ceria and zirconia contents were studied in this article to evaluate the effect of the support reducibility and metal dispersion on the stability of the catalyst on partial oxidation of methane reaction.
135 citations
TL;DR: In this paper, the surface and sub-surface oxidation of dispersed copper phase by N2O adsorptive decomposition at controlled temperature followed by H2 temperature-programmed reduction of the Cu2O surface layers formed (s-TPR) was performed on siliceous supported catalysts.
Abstract: Surface and sub-surface oxidation of dispersed copper phase by N2O adsorptive decomposition at controlled temperature followed by H2 temperature-programmed-reduction of the Cu2O surface layers formed (s-TPR) was performed on siliceous supported catalysts (ca. 6 wt.% Cu). The combined analysis permitted to measure the copper dispersion and to identify different surface copper species. Copper dispersion parameters were calculated from the H2-uptakes in the back-titration of the oxygen atoms fixed on the Cu particles by the s-TPR analysis. S-shaped curves were obtained plotting the H2-uptakes versus N2O oxidation temperature, the change of slope could indicate the beginning of copper deep oxidation, ca. 70 °C, that continued up to bulk oxidation at higher temperatures. Extrapolation of the H2-uptake to “zero-temperature” allowed calculating the “true” copper dispersion ( D Cu * ) and related parameters. In addition, s-TPR provided qualitative and quantitative reduction profiles of the copper surface species. Besides Cu2O, formed by N2O oxidation of Cu(0) particles, copper species strongly interacting with support were clearly individuated as a function of the support nature.
129 citations
TL;DR: In this paper, two synthetic approaches to the preparation of Au/Fe2O3 nanocatalysts were compared: a novel deposition-precipitation technique utilizing thermal decomposition of urea and the conventional coprecipitation method.
Abstract: Two synthetic approaches to the preparation of Au/Fe2O3 nanocatalysts were compared: a novel deposition–precipitation technique utilizing thermal decomposition of urea and the conventional coprecipitation method. The products were characterized by X-ray powder diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), and temperature programmed reduction. The catalysts prepared by both methods demonstrated very high activity toward CO oxidation in the “as prepared” state. Starting with the same amount of gold precursor, the deposition–precipitation technique produces a catalyst with higher final gold content than the coprecipitation method because it achieves more complete precipitation of the gold from solution. Heat treatment of the samples prepared by both methods resulted in a decrease of the catalytic activity by about an order of magnitude. However, we conclude that heat-treated Au/Fe2O3 catalysts are more suitable for practical applications because of stability issues with the “as prepared” samples.
116 citations
TL;DR: In this article, bimetallic palladium-platinum nanoparticles supported on alumina were prepared by flame spray pyrolysis and tested for catalytic combustion of methane with a focus on the thermal stability of the noble metal particles.
Abstract: Bimetallic palladium–platinum nanoparticles supported on alumina were prepared by flame spray pyrolysis. The as-prepared materials were characterized by scanning transmission electron microscopy (STEM), CO chemisorption, nitrogen adsorption (BET), X-ray diffraction (XRD), temperature programmed reduction (TPR), thermogravimetric analysis (TGA) and extended X-ray absorption fine structure (EXAFS) spectroscopy. The materials were tested for the catalytic combustion of methane with a focus on the thermal stability of the noble metal particles. After flame synthesis the noble metal components of the materials were predominantly in oxidized state and finely dispersed on the alumina matrix. Reduction afforded small bimetallic Pd–Pt alloy particles (< 5 nm) supported on Al2O3 ceramic nanoparticles. The addition of small amounts of platinum made the palladium particles more resistant against sintering at high temperatures and further lowered the deactivation observed during methane combustion.
106 citations
TL;DR: This study involved an investigation of the thermal stability and reactions of nitrogen surface functional groups in nanoporous carbons and results are discussed in terms of decomposition ranges for surfacefunctional groups and reaction mechanisms of surface species.
Abstract: The reactions of surface functional groups have an important role in controlling conversion of char nitrogen to NOx during coal combustion. This study involved an investigation of the thermal stability and reactions of nitrogen surface functional groups in nanoporous carbons. Four suites of carbons, which were used as models for coal chars, were prepared with a wide range of nitrogen and oxygen contents and types of functional groups. The porous structures of the carbons were characterized by gas adsorption methods while chemical analysis, X-ray photoelectron spectroscopy, and X-ray near edge structure spectroscopy were used to characterize the surface functional groups. Temperature programmed desorption and temperature programmed reduction methods were used to study the reactivity of the surface functional groups during heat treatment under inert and reducing conditions. Heat treatment studies show that the order of stability of the functional groups is quaternary nitrogen > pyridinic > pyrrolic > pyridine N-oxide. Pyridine N-oxide surface groups desorb NO and form N2 via surface reactions at low temperature. Pyrrolic and pyridinic functional groups decompose and react with surface species to give NH3, HCN, and N2 as desorption products, but most pyrrolic groups are preferentially converted to pyridinic and quaternary nitrogen. The main desorption product is N2. Approximately 15-40 wt % of the original nitrogen was retained in the carbons mainly as quaternary nitrogen after heat treatment to 1673 K. The results are discussed in terms of decomposition ranges for surface functional groups and reaction mechanisms of surface species.
91 citations
TL;DR: In this paper, catalysts were prepared from hydrotalcite precursors, characterized and tested in the reaction of methane steam reforming to produce hydrogen, and the catalytic tests demonstrated high methane conversion, high activity for hydrogen production and high stability during the time of reaction for a molar ratio in the feed H2O:CH4 = 2:1.
TL;DR: In this article, a washcoating procedure was developed and explained on the basis of a copper catalyst system by the use of dispersed nanoparticles, and the mixing of CuO particles with other necessary materials like ZnO was examined during high energy ball milling or dispersing the powders in a solution of cellulose derivatives.
Abstract: The demand of fast load alternations for hydrogen generation by methanol steam reforming for automotive fuel cell application may be met in an excellent manner by microstructured reactors. However, catalyst incorporation is difficult in the micrometer size. By the use of dispersed nanoparticles a washcoating procedure was developed and is explained on the basis of a copper catalyst system. The mixing of CuO particles with other necessary materials like ZnO was examined during high energy ball milling (dry mixing) or dispersing the powders in a solution of cellulose derivatives (wet mixing). For the latter technique the shearing of agglomerates and re-agglomeration were investigated for the pure substances using laser diffraction. The influence of ball milling on particle sizes was determined by adsorption experiments and X-ray diffraction. All mixtures were characterized by temperature programmed reduction (TPR) followed by the measurement of the Cu(0) particle size (X-ray diffraction). A special method based upon X-ray structure analysis was applied for determination of the mixing quality. The relationship between these catalyst properties and additional measurements of the catalyst activity/degradation done was obvious.
TL;DR: In this paper, the deactivation and regeneration of a model Pt/Ba/Al2O3 NOx trap catalyst is studied by hydrogen temperature programmed reduction (TPR), X-ray diffraction (XRD), and NOx storage capacity measurements.
Abstract: The deactivation by sulfur and regeneration of a model Pt/Ba/Al2O3 NOx trap catalyst is studied by hydrogen temperature programmed reduction (TPR), X-ray diffraction (XRD), and NOx storage capacity measurements. The TPR profile of the sulfated catalyst in lean conditions at 400 °C reveals three main peaks corresponding to aluminum sulfates (∼550 °C), “surface” barium sulfates (∼650 °C) and “bulk” barium sulfates (∼750 °C). Platinum plays a role in the reduction of the two former types of sulfates while the reduction of “bulk” barium sulfates is not influenced by the metallic phase. The thermal treatment of the sulfated catalyst in oxidizing conditions until 800 °C leads to a stabilization of sulfates which become less reducible. Stable barium sulfides are formed during the regeneration under hydrogen at 800 °C. However, the presence of carbon dioxide and water in the rich mixture allows eliminating more or less sulfides and sulfates, depending on the temperature and time. The regeneration in the former mixture at 650 °C leads to the total recovery of the NOx storage capacity even if “bulk” barium sulfates are still present on the catalyst.
TL;DR: In this paper, the reduction of Co 3+ in LaCoO 3 to Co 0 belongs to a one-step process and that every TPR peak represents a reduction of every co 3+ species to Co 1 in the crystallite structure.
TL;DR: In this article, an autothermal reforming (ATR) of n -octane was addressed based on thermodynamic analysis and carried out on a non-pyrophoric catalyst 0.3.
Abstract: In an attempt to effectively integrate catalytic partial oxidation (CPO) and steam reforming (SR) reactions on the same catalyst, autothermal reforming (ATR) of n -octane was addressed based on thermodynamic analysis and carried out on a non-pyrophoric catalyst 0.3 wt.% Ru/K 2 O-CeO 2 /γ-Al 2 O 3 . The ATR of n -octane was more efficient at the molar ratio of O 2 /C 0.35–0.45 and H 2 O/C 1.6–2.2 (independent parameters), respectively, and reforming temperature of 750–800 °C (dependent parameter). Among the sophisticated reaction network, the main reaction thread was deducted as: long-chain hydrocarbon → CH 4 , short-chain hydrocarbon → CO 2 , CO and H 2 formation by steam reforming, although the parallel CPO, decomposition and reverse water gas shift reaction took place on the same catalyst. Low temperature and high steam partial pressure had more positive effect on CH 4 SR to produce CO 2 other than CO. This was verified by the tendency of the outlet reformate to the equilibrium at different operation conditions. Furthermore, the loss of active components and the formation of stable but less active components in the catalyst in the harsh ATR atmosphere firstly make the CO inhibition capability suffer, then eventually aggravated the ATR performance, which was verified by the characterizations of X-ray fluorescence, BET specific surface areas and temperature programmed reduction.
TL;DR: Several compositions of palladium-loaded calcium hydroxyapatite Pd(x)/CaHAp were prepared and characterized by XRD, IR, and UV-visible spectroscopy and temperature-programmed reduction.
TL;DR: In this paper, a series of MCM-41 supports modified with phosphorus (0.5 -1.5 ) and their respective NiMo catalysts were prepared and characterized by N2 physisorption, XRD, ammonia TPD, temperature programmed reduction (TPR), UV-vis diffuse reflectance spectroscopy (DRS), chemical analysis and HRTEM.
TL;DR: In this article, small palladium nanoparticles supported on lanthanum-stabilized alumina were prepared by flame spray pyrolysis and tested for catalytic combustion of methane with a focus on the thermal stability of the support and the palladium particles.
Abstract: Palladium nanoparticles supported on lanthanum-stabilized alumina were prepared by flame spray pyrolysis. The as-prepared materials were characterized by high-resolution transmission electron microscopy, CO chemisorption, nitrogen adsorption, X-ray diffraction and temperature programmed reduction. These materials were tested for the catalytic combustion of methane with a focus on the thermal stability of the support and the palladium particles. Flame spray pyrolysis afforded small palladium particles (<5 nm) attached to the surface of the supporting La2O3/Al2O3 ceramic nanoparticles with specific surface areas in the range of 50–180 m2 g−1. Compared to commercial reference materials the flame-made catalysts showed excellent thermal stability in terms of specific surface area up to 1200 °C and retarded γ- to α-alumina transformation. Catalysts were tested as-prepared (small Pd particles, <5 nm) and after sintering at 1000 °C (large Pd particles, 50–150 nm). By cycling the temperature several times from 200 to 1000 °C during catalytic combustion, it could be shown that all catalytic materials, regardless of specific surface area, lanthanum content, and preparation method (flame-synthesis or impregnated), exhibited similar catalytic performance after an initial conditioning cycle.
TL;DR: SBA-15 was synthesized and used as support for a Ni catalyst prepared by deposition-precipitation (D-P), and the results showed that, at the Ni loading used here (10.3% Ni), SBA15 preserves its hexagonal porous arrangement as discussed by the authors.
TL;DR: In this paper, the CoNdOx (CoNdO3 perovskite-type mixed metal oxide was used for the carbon-free CO2 reforming of methane.
Abstract: CoNdOx (Co/Nd = 1) is a highly promising catalyst for the carbon-free CO2 reforming of methane. Influence of the Co/Nd ratio on the catalyst performance in the CO2 reforming and also on the crystalline phases and reduction by temperature programmed reduction (TPR) of the CoNdOx catalyst has also been investigated. The CoNdOx (CoNd = 1.0) catalyst consisted of mainly NdCoO3 perovskite-type mixed metal oxide and it showed not only a high resistance to carbon formation at different process conditions (viz. temperature = 750–900 °C and gas hourly space velocity (GHSV) = 10000–50000 cm3 g−1 h−1) but also high activity and selectivity in the CO2 reforming process. The high resistance to carbon formation for this catalyst is attributed mostly to strong metal (Co°)–support (Nd2O3) interactions.
TL;DR: In this article, different morphologies of silver nanoparticles affect the selective oxidation of styrene in the gas phase using oxygen as oxidant, and the promotion effect on the catalytic activity of potassium and cesium on the silver nanowires catalysts was also studied.
TL;DR: In this article, the effect of cerium on the properties of zirconia-supported platinum catalysts was studied in the water gas shift reaction (WGSR) at high temperatures (320-450°C) over hematite-based catalysts doped with chromium.
TL;DR: In this paper, the temperature profiles of the catalyst bed were studied using an infrared (IR) thermograph, and it was shown that the temperature at the inlet is much higher under CH4/H2O/O2/Ar = 20/10/20/50 than under CH 4/H 2O/N 2 O 2 N = 10/0/20 /70.
Abstract: During the reactions related to oxidative steam reforming and combustion of methane over α-alumina-supported Ni catalysts, the temperature profiles of the catalyst bed were studied using an infrared (IR) thermograph. IR thermographical images revealed an interesting result: that the temperature at the catalyst bed inlet is much higher under CH4/H2O/O2/Ar = 20/10/20/50 than under CH4/H2O/O2/Ar = 10/0/20/70; the former temperature is comparable to that over noble metal catalysts such as Pt and Pd. Based on the temperature-programmed reduction and oxidation measurements over fresh and used catalysts, the metallic Ni is recognized at the catalyst bed inlet under CH4/H2O/O2/Ar = 20/10/20/50, although it is mainly oxidized to NiAl2O4 under CH4/H2O/O2/Ar = 10/0/20/70. This result indicates that the addition of reforming gas (CH4/H2O = 10/10) to the combustion gas (CH4/O2 = 10/20) can stabilize Ni species in the metallic state even under the presence of oxygen in the gas phase. This would account for its extremely high combustion activity.
TL;DR: In this article, the effect of the preparation method of Pt/CeZrO2/Al2O3 catalysts on the dispersions of the metal and of the ceria-zirconia on the surface of the alumina and on the catalytic performance of methane partial oxidation reaction was evaluated.
TL;DR: In this paper, the effects of tin and potassium addition on the catalytic properties of Pt/SiO 2 catalysts were studied by diffuse reflectance UV-vis spectroscopy, temperature programmed reduction (TPR), CO chemisorption and isobutane dehydrogenation.
Abstract: The effects of tin and potassium addition on the catalytic properties of Pt/SiO 2 catalysts were studied by diffuse reflectance UV–vis spectroscopy, temperature programmed reduction (TPR), CO chemisorption and isobutane dehydrogenation. Pt/SiO 2 , Sn/SiO 2 and Pt–Sn/SiO 2 catalysts were prepared by incipient wetness impregnation with aqueous solutions of H 2 PtCl 6 and SnCl 2 . Pt–Sn/SiO 2 catalysts were prepared by coimpregnation and sequential impregnation. A part of these catalysts was then impregnated with an aqueous solution of KOH. Fresh and calcined catalysts were studied. [PtCl 2 (SnCl 3 ) 2 ] 2− complex was only detected in (PtSn/SiO 2 ) and Sn(Pt/SiO 2 ) catalysts. The proximity between Pt and Sn species favoured the formation of Pt–Sn ensembles or alloys after the reduction treatment that provided stability and selectivity for the isobutane dehydrogenation. The addition of potassium to fresh Pt–Sn/SiO 2 did not change the activity, but it improved the dehydrogenation selectivity, which reached values of almost 100%. Surface Pt–Sn species changed by the calcination treatment, causing the segregation of Pt and Sn oxide species. This treatment caused a decrease of CO/Pt ratio, activity and selectivity of Pt–Sn catalysts. In calcined Pt–Sn–K catalysts, the activity seemed to be a function of K–Pt–Sn interactions.
TL;DR: In this article, the influence of Sn addition on the catalytic activity of Pt-Re/Al 2 O 3 naphtha reforming catalysts was studied and the acid function of the catalysts were studied by means of temperature programmed desorption of pyridine and the reaction test of n -pentane isomerization.
TL;DR: In this article, the performance of Pd/CeO 2 and Sm 2 O 3 (Pd/CS) catalysts in steam reforming of methanol as well as their physicochemical properties were investigated.
Abstract: With a view to their use as catalytic anode materials for direct methanol solid oxide fuel cells (DM-SOFCs), the performance of Pd/CeO 2 –Sm 2 O 3 (Pd/CS), Pd/CeO 2 and Pd/Sm 2 O 3 catalysts in the steam reforming of methanol as well as their physicochemical properties – analyzed by N 2 adsorption, XRD, temperature programmed reduction (TPR), CO chemisorption and X-ray photoelectron spectroscopy (XPS) – have been investigated. The catalytic activity in methanol steam reforming was evaluated in a tubular microreactor at atmospheric pressure in the 300–500 °C reaction temperature interval (space velocity = 0.32 mol/(h g cat ), H 2 O/CH 3 OH molar ratio = 1.2, methanol concentration 15 mole%). H 2 , CO and CO 2 were the main reaction products. Methanol conversions up to 72% and H 2 productivities as high as 0.46 mol/(h g cat ) were obtained on the Pd/CS catalyst. Moreover, low H 2 productivity (0.09 mol/(h g cat )) was found on the Pd/CeO 2 catalyst, while Pd/Sm 2 O 3 appeared to be inactive. This behaviour can be partly assigned to the higher dispersion and the more favourable distribution of Pd particles observed in the Pd/CS catalyst. A strong association of Pd and samarium oxide and an enrichment in both components at the external surface of the Pd/CS catalyst grains was found by means of TPR and XPS. This could be explained by the partial dissolution of Sm 2 O 3 in the acid medium used during catalyst preparation leading to the re-precipitation of a Pd/Sm-containing phase. Higher activity per exposed Pd atom was also observed for the Pd/CS catalyst. This was attributed to enhancement of diffusion and adsorption of reactants on the basic sites of the Sm-containing support.
TL;DR: Palladium, silver and palladium-silver catalysts supported on silica were prepared by co-consumption of support with solution of AgNO3 and Pd(NO3)2.
Abstract: Palladium, silver and palladium–silver catalysts supported on silica were prepared by coimpregnation of support with solution of AgNO3 and Pd(NO3)2. The catalysts were characterized by X-ray powder diffraction (XRD), temperature programmed reduction (TPR), time of flight ion mass spectrometry (ToF-SIMS), chemisorption of carbon monoxide and were tested in the reaction of selective oxidation of glucose to gluconic acid. XRD and TPR studies have shown that an interaction between Pd and Ag on the surface of silica after oxidation at 500 °C and reduction at 260 °C leads to the formation of solid solutions. ToF-SIMS images of the surface of 5% Ag/SiO2 catalyst after oxidation at 500 °C and reduction at 260 °C show that Ag atoms supported on silica are not distributed homogenously but tend to form regions of enhanced Ag concentration. Positive ions images of the surface of 5% Pd/SiO2 catalyst also display regions of enhanced concentration of Pd atoms, but they are more homogenously distributed on silica. ToF-SIMS peak intensity ratio 108Pd+/107Ag+ for bimetallic 5% Pd–5% Ag/SiO2 catalysts has a lower value than that obtained for physical mixture 5% Pd/SiO2–5% Ag/SiO2 which indicates that the surface of bimetallic catalyst is enriched with silver atoms.
TL;DR: In this paper, the mechanisms involved in NO-char heterogeneous reduction were studied with a synthetic coal (SC) char as carbon source, and the main products of the NO-C reaction were found to be N 2 and CO 2.
TL;DR: In this paper, the performance and its relation with the structure of a highly loaded Co/SiO2 catalyst in the gas phase hydrogenation of crotonaldehyde when varying the thermal treatments to which the catalyst precursor has been subjected.
Abstract: This paper reports on the performance and its relation with the structure of a highly loaded (41 wt.%) Co/SiO2 catalyst in the gas phase hydrogenation of crotonaldehyde when varying the thermal treatments to which the catalyst precursor has been subjected. The optimum calcination and reduction temperatures were identified where the highest selectivity to crotyl alcohol (around 90%) was obtained with the catalyst calcined at 400 °C and reduced at 350 °C even at conversions as high as 60%. Higher temperature of calcination was found to lower the crotyl alcohol selectivity. Both, lower and higher reduction temperatures will not favour the crotyl alcohol formation. These results were interpreted and correlated with the surface structure of the catalyst which was shown by temperature programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS) analysis. Depending on the thermal conditions imposed, the surface consisted of either Co metal, or coexisting metal and its oxide; structure which favours the high crotyl alcohol selectivity. By TEM analysis, large particles (diameter exceeding 50 nm) were identified after reduction at 350 °C. A global activation energy of 44 kJ/mol was obtained with this catalyst. In the light of the obtained results a discussion on the reaction mechanism involving metal, metal-oxide double sites has been put forward. It was emphasised that, for selective hydrogenation of crotonaldehyde into unsaturated alcohol, Co catalysts compete favourably with platinum based catalysts.