Ru Particle Size Research Articles

The action mechanism of ethanol in preparation of supported nano-sized Ru catalyst via supercritical fluid deposition

Ru catalysts supported on activated carbon (AC) were prepared by supercritical fluid deposition (SFD) with ethanol added and their catalytic performance in butanone hydrogenation was investigated. The effects of ethanol amount on Ru particle size were systematically studied. As the amount of ethanol increased, Ru mean particle sizes always decreased firstly, then increased. And the minimum mean particle size of Ru was obtained at 10ml ethanol. The catalysts with smaller Ru mean particle size presented higher catalytic activity. These results demonstrated that the role of ethanol may not be only co-solvent but also anti-solvent and extractant during the preparation of Ru/AC.

Evidences of Two‐Regimes in the Measurement of Ru Particle Size Effect for CO Dissociation during Fischer–Tropsch Synthesis

AbstractThis work assesses the effect of the particle size for the Fischer–Tropsch synthesis with catalysts based on Ru particles between 4 and 71 nm. CO dissociation is a structure‐sensitive reaction, that is, the turnover frequency (TOF) is affected by Ru particle size. Herein it is demonstrated that two regimes exist for the effect of Ru particle size. On the one hand, the expected relationship of TOF with particle size, that is, the TOF increases with Ru particles <10 nm, is only observed if measured at steady‐state conditions. On the contrary, the TOF increases constantly with Ru particle size if measured at the initial state. However, the TOF measured for catalysts with Ru particles >10 nm declines during time on stream. These observations suggest that two regimes for the measurement of CO dissociation exist during Fischer–Tropsch synthesis. The reason for this is that two sites for CO dissociation on the Ru particles >10 nm exist at the initial state, terraces and step‐edges, but the latter ones deactivate during time on stream.

Influence of pretreatment on the catalytic performance of Ru/SBA-15 catalysts for glycerol hydrogenolysis

Ru/SBA-15 catalysts were prepared by impregnation and were pretreated under different conditions, and were characterized by N 2 adsorption-desorption, X-ray diffraction, CO chemisorption, transmission electron microscopy, and the reaction of glycerol hydrogenolysis. The catalyst calcined in air had larger Ru particles, while the direct reduction of the catalysts with H 2 without air pre-calcination made the Ru particles dispersed well. As the H 2 reduction temperature increased, the Ru dispersion decreased. The turnover frequency (TOF) of the catalysts increased as the Ru dispersion decreased, indicating that Ru/SBA-15 catalyzed glycerol hydrogenolysis is a structure sensitive reaction. Different treatment conditions gave Ru/SBA-15 catalysts with different Ru particle size, and they showed that glycerol hydrogenolysis over Ru/SBA-15 is a structure sensitive reaction.

Highly dispersed Ru on K-doped meso–macroporous SiO2 for the preferential oxidation of CO in H2-rich gases

In this work, highly dispersed Ru nanoparticles which had a uniform small nanoparticle size were supported on K-promoted meso–macroporous SiO2 by using the simple impregnation method. The effect of the size of Ru nanoparticle on the catalytic performance for the preferential oxidation of CO (CO-PROX) in H2-rich gases was investigated. Meanwhile, the related mechanism on size effect was discussed. The catalysts were characterized by using techniques of transmission electron microscopy, temperature-programmed reduction and CO-chemisorption. The results indicate that the K-promoted Ru/SiO2 catalyst with the size of metal Ru particles at about 7 nm showed obviously higher turnover frequency (TOF) than that of K-Ru/SiO2 with smaller size of Ru particles of around 2 nm. As for oxidizing CO to CO2 on specific weight of ruthenium, the catalyst with the smaller size of metal Ru exhibited better performance owing to its much higher specific surface area of metal Ru. The catalyst with the smaller size of Ru nanoparticles showed much better methanation formation resistance for CO and CO2. The K-promoted and highly dispersed Ru on SiO2 exhibited excellent activity and selectivity for the CO-PROX reaction.

Catalytic supercritical water gasification of proteinaceous biomass: Catalyst performances in gasification of ethanol fermentation stillage with batch and flow reactors

The catalytic supercritical water gasification (SCWG) characteristics of ethanol fermentation stillage as a model for proteinaceous biomass were examined using batch and flow reactors. Batch reactions conducted at 385°C and 26MPa found that certain Ni and Ru catalysts gave almost 100% carbon conversion within 60min of reaction time, while non-catalyzed reactions gave only 10% conversion for the same duration. Ru generally showed higher catalytic activity per mass of catalyst metal than Ni. Control of the extent of reaction by changing the reaction time and catalyst amount showed that in the case of supported Ru catalysts, major gas component yields (CH4 and CO2) exhibited respective universal dependence against total carbon yield, despite the varied support materials and Ru particle sizes used. This is an indication that the present reaction system is structure-insensitive with respect to supported Ru catalysts. For repetitive batch reactions, Raney-type Ni catalysts were more stable than supported Ni or Ru catalysts. A modified Raney Ni catalyst that showed better durability than non-modified one in batch reactions did not show advantages in flow reactions, which could be explained by the differences in reaction environment with respect to the two types of reactors. The SCWG reaction pathways of ethanol stillage are discussed in relation to the steam reforming mechanism; the reason for the appearance of minor amounts of C2+ species in the product gas stream, which is not expected from the steam reforming mechanism, is discussed.

Ru/ZrO<sub>2</sub>催化剂在苯部分加氢反应中的粒径效应

The particle size effect on partial hydrogenation of benzene to cyclohexene over Ru/ZrO2 catalysts is reported. Uniform Ru nanoparticles (NPs) with a tunable particle size from 2.4 to 5.4 nm were synthesized by a polyol reduction method and deposited on ZrO2. The catalysts were characterized by ultraviolet-visible absorption spectroscopy (UV-Vis), N2 physisorption, H2 chemisorption, temperature-programmed desorption of H2 (H2-TPD), powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). It was found that the type of polyol and the concentration of additive (sodium acetate trihydrate) imposed remarkable effect on the particle size of Ru. A distinct particle size effect occurred in partial hydrogenation of benzene. With the size of the Ru NPs increasing, the hydrogenation activity of benzene increased, and the initial selectivity ( S 0) to cyclohexene showed a volcanic-type variation tendency, which revealed that the optimal Ru size for obtaining the highest S 0 is 4.4 nm. The Ru/ZrO2 catalyst reduced by 1,2-propanediol exhibited the highest S 0 (82%) and the yield of cyclohexene (39%). Based on the characterization results, the size effect of Ru on the activity and selectivity is discussed.

Preparation of Ru nanoparticles on TiO2using selective deposition method and their application to selective CO methanation

Selective CO methanation was investigated over Ru/TiO2 prepared using a selective deposition method with NaOH and NH3 aqueous solution as a pH adjuster. Control of pH by NH3 solution resulted in the small particle size of Ru (average 1.2 nm) and the formation of Na-free Ru/TiO2, leading to high CO methanation activity and a wide temperature window for selective CO methanation at low temperatures.

Hydrogenation of succinic acid to tetrahydrofuran (THF) over ruthenium–carbon composite (Ru–C) catalyst

Ruthenium–carbon composite (Ru–XC) catalysts prepared by a single-step surfactant-templating method were pre-graphitized at different temperature (X=200, 250, 300, 350, and 400°C), and they were applied to the liquid-phase hydrogenation of succinic acid to tetrahydrofuran (THF). The effect of pre-graphitization temperature on the catalytic performance of Ru–XC catalysts (X=200, 250, 300, 350, and 400°C) was investigated. It was observed that Ru–XC composite catalysts showed different textural properties depending on pre-graphitization temperature. In the liquid-phase hydrogenation of succinic acid to tetrahydrofuran (THF), conversion of succinic acid and yield for THF showed volcano-shaped trends with respect to pre-graphitization temperature. In other words, an optimal pre-graphitization temperature was required to achieve maximum catalytic performance of Ru–XC catalysts. Yield for THF in the hydrogenation of succinic acid increased with decreasing ruthenium particle size of Ru–XC catalysts. Among the catalysts tested, Ru-300C, which had the smallest ruthenium particle size, showed the highest yield for THF.

Ruthenium catalyst supported on high-surface-area basic ZrO2 for ammonia synthesis

The superbasic ZrO2 (ZrO2-KOH) with high surface area was prepared by reflux-digestion of ZrO(OH)2 gel in mother liquor and examined as a support promoting ammonia synthesis by particulate Ru. The TEM image of Ru/ZrO2-KOH catalyst indicates that the size of Ru particles is in the range of 1.5–3.2nm, which is the optimum size of Ru particles for the maximum number of B5-type sites. Additionally, the characterizations including CO2-TPD, XPS and N2-TPD demonstrate that the Ru particles supported on ZrO2-KOH exhibit higher electron density compared to that of Ru/ZrO2 catalyst. As a result, the dissociative adsorption of N2 over Ru/ZrO2-KOH is more facile than that over Ru/ZrO2 catalyst. Thus, the Ru/ZrO2-KOH catalyst shows an excellent activity for ammonia synthesis especially under the conditions of low temperature and pressure. The highest reaction rate of Ru/ZrO2-KOH is 16.91mmol/(gh) at 698K and 3.0MPa, which is much higher than that of various Ru catalysts supported on other supports.

Catalytic properties of Ru nanoparticles embedded on ordered mesoporous carbon with different pore size in Fischer-Tropsch synthesis

A series of 3 wt% Ru embedded on ordered mesoporous carbon (OMC) catalysts with different pore sizes were prepared by autoreduction between ruthenium precursors and carbon sources at 1123 K. Ru nanoparticles were embedded on the carbon walls of OMC. Characterization technologies including power X-ray diffraction (XRD), nitrogen adsorption-desorption, transmission electron microscopy (TEM), and hydrogen temperature-programmed reduction (H2-TPR) were used to scrutinize the catalysts. The catalyst activity for Fischer-Tropsch synthesis (FTS) was measured in a fixed bed reactor. It was revealed that 3 wt% Ru-OMC catalysts exhibited highly ordered mesoporous structure and large surface area. Compared with the catalysts with smaller pores, the catalysts with larger pores were inclined to form larger Ru particles. These 3 wt% Ru-OMC catalysts with different pore sizes were more stable than 3 wt% Ru/AC catalyst during the FTS reactions because Ru particles were embedded on the carbon walls, suppressing particles aggregation, movement and oxidation. The catalytic activity and C5+ selectivity were found to increase with the increasing pore size, however, CH4 selectivity showed the opposite trend. These changes may be explained in terms of the special environment of the active Ru sites and the diffusion of products in the pores of the catalysts, suggesting that the activity and hydrocarbon selectivity are more dependent on the pore size of OMC than on the Ru particle size.

Aqueous phase reforming of ethanol and acetic acid over TiO2 supported Ru catalysts

This study examined the dependence of Ru particle sizes upon the activity and selectivity for aqueous phase reforming reactions of ethanol and acetic acid over Ru/TiO2 at 473K. For ethanol, irrespective of the Ru particle size, the 1:1 ratio of CH4 and CO2 was formed at the initial stage, indicating the absence of complete reforming with water. At the later stage, unfavorable methanation of CO2 by H2 was observed over larger Ru particle catalysts. That methanation was suppressed completely over smaller Ru particle catalysts. In the case of acetic acid reforming over smaller Ru particle catalysts, a 2:1 ratio of H2 and CO2 was formed constantly, indicating the operation of complete reforming reaction with water. Positively charged small Ru particles were responsible for the efficient activation of acetic acid and water to form H2 and CO2 selectively.

Advances in small-angle X-ray scattering for the study of supported catalysts

Ru particle sizes in supported ruthenium catalysts have been studied by small-angle X-ray scattering (SAXS). It has been proposed to use new masking liquids with a relatively low X-ray radiation absorption. Using these liquids it was possible to achieve practically quantitative agreement between SAXS and transmission electron microscopy data. The SAXS technique employing such masking liquids can be used as a quick analytical method for determining the particle size distributions of supported metals. Fluorocarbon liquids can eliminate the scattering signal from any support with a density of 2.5 g cm−3or less. This procedure can be very useful for selective study of separate components in complex samples consisting of carbon materials, silica materials, polymers, some hydroxides, claysetc.

Effect of treatment conditions on ruthenium particle size and ammonia synthesis activity of ruthenium catalyst

Ru/Al2O3 catalysts with different Ru particle sizes were prepared by changing the metal loading, the treatment temperature in hydrogen or the calcination temperature in air. It is found that the catalysts obtained by different methods cannot directly be used to study the correlation between particle sizes and the catalytic activity. The difference in treatment conditions of Ru/Al2O3 catalysts affected the ammonia synthesis activity of Sm-promoted Ru/Al2O3 not only by affecting the sizes and the shapes of Ru particles, but also by changing the properties of some active sites available for gas adsorption.

Highly effective perovskite-type BaZrO3 supported Ru catalyst for ammonia synthesis

The ammonia synthesis was performed over Ru catalyst supported on perovskite-type BaZrO3. Physiochemical properties of this catalyst were also characterized by means of various techniques to show the relationships between catalyst structure and catalytic performance. It was found that the ammonia concentration in the effluent of Ru/BaZrO3 catalyst was 6.36% at 673K under 3.0MPa, which was much higher than that of Ru catalyst supported on other supports including carbon material systems under the similar conditions, and the rate did not decrease even if the reaction was executed for 120h. This might be attributed to the facts that the optimum size of Ru particles has more B5-type sites, strong electron-donating ability of the BaZrO3 support and the strong metal–support interaction provides an efficient channel for electron transfer. On the other hand, the adsorption of H2 was inhibited over the surface of this catalyst and the number of active sites for the activation of N2 was also increased.

Ru particle size effect in Ru/CNT-catalyzed Fischer-Tropsch synthesis

Carbon nanotube (CNT)-supported Ru nanoparticles with mean sizes ranging from 2.3 to 9.2 nm were prepared by different post-treatments and studied for Fischer-Tropsch (FT) synthesis. The effects of Ru particle size on catalytic behaviors were investigated at both shorter and longer contact times. At shorter contact time, where the secondary reactions were insignificant, the turnover frequency (TOF) for CO conversion was dependent on the mean size of Ru particles; TOF increased with the mean size of Ru particles from 2.3 to 6.3 nm and then decreased slightly. At the same time, the selectivities to C5+ hydrocarbons increased gradually with the mean size of Ru particles up to 6.3 nm and then kept almost unchanged with a further increase in Ru particle size. At longer contact time, C10–C20 selectivity increased significantly at the expense of C21+ selectivity, suggesting the occurrence of the selective hydrocracking of C21 + to C10–C20 hydrocarbons.

Study of potassium promoter effect for Ru/AC catalysts for ammonia synthesis

Ru/AC catalysts with K promoter were prepared by impregnation of the samples with different amounts of KOH. The catalysts were characterized using a variety of techniques, including X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, CO chemisorption and temperature-programmed desorption. The presence of K promoter had a limited effect on the size of Ru particles, but significantly enhanced the amount of adsorbed hydrogen, nitrogen and ammonia. A new desorption peak of nitrogen and ammonia at low temperature can be observed in their TPD profiles for Ru catalysts with K promoter. We propose that the presence of K promoter not only improved the adsorption properties of hydrogen, nitrogen and ammonia for Ru catalyst supported on activated carbon, but also weakened the adsorption strength of nitrogen and ammonia. The change in the chemisorptive properties of reactant gases including hydrogen, nitrogen and ammonia may be responsible for K promoter enhanced ammonia synthesis activity of Ru/AC catalyst, more than just the electronic properties of K promoter.

Hydrodenitrogenation of Pyrrole over Silica-supported Ruthenium Phosphide Catalyst

Catalytic properties of ruthenium phosphide (Ru2P) supported on silica for hydrodenitrogenation (HDN) of pyrrole were compared with those of Ru/SiO2 catalyst to clarify the effect of phosphidation. At higher W/F (652 g h mol−1), pyrrole conversion over Ru/SiO2 catalyst remarkably decreased with increasing reduction temperature. In contrast, pyrrole conversion over P-added Ru (Ru–P/SiO2) catalyst at the same W/F was enhanced with increasing reduction temperature due to Ru2P formation. This activity was higher than that of sulfided NiMoP/Al2O3 catalyst but lower than that of Ru/SiO2 catalyst at the same W/F. At lower W/F (130-391 g h mol−1), Ru–P/SiO2 catalyst showed higher activity and stability for pyrrole HDN than Ru/SiO2 catalyst. The cracking products (almost all CH4) were formed over Ru/SiO2 catalysts and butanes were formed over Ru–P/SiO2 catalysts. The results of CO adsorption and TEM images revealed that the particle size of Ru–P/SiO2 catalyst was smaller than that of Ru/SiO2 catalyst. The TOF of Ru–P/SiO2 catalyst increased with reduction temperature, and this TOF was lower than that of Ru/SiO2 catalyst. After HDN reaction, the peak of particle size distribution for Ru/SiO2 catalyst shifted to larger diameter, whereas that of Ru–P/SiO2 catalyst remained the same. Therefore, the stable activity of Ru–P/SiO2 catalyst can be explained by excess phosphorus species acting to stabilize Ru2P particles.

Selective CO methanation in CO2-rich H2 atmospheres over a Ru/zeolite catalyst: The influence of catalyst calcination

The pre-treatment of highly active and selective Ru/zeolite catalysts for the selective CO methanation in CO2-rich H2 atmospheres involves a calcination step before the catalyst activation to reach their high activity and selectivity. In this study, we investigated the impact of the calcination procedure on a 2.2wt.% Ru/zeolite catalyst by evaluating the resulting changes in the catalyst structure and reaction characteristics by combined kinetic, in situ extended X-ray absorption fine structure (EXAFS) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements. Calcination in synthetic air, followed by the standard activation procedure in reaction gas, results in a decrease in mean Ru particle size with increasing calcination temperature, from ∼1.5nm to ∼1.0nm. The increase in dispersion goes along with a distinct increase in selectivity of the Ru/zeolite catalyst for CO methanation at extremely low concentrations of CO (100ppm). Possible mechanisms and the physical origin responsible for these changes in catalyst structure and reaction characteristics are discussed.

Activity and deactivation nature of Ru/MnCO3 catalysts for Fischer–Tropsch reaction

The catalytic activities and different behaviors for catalyst deactivation by forming surface hydrocarbon deposits were investigated on the Cl-free Ru/MnCO3 Fischer–Tropsch synthesis (FTS) catalysts in a low pressure fixed-bed reactor. Catalytic activity of LT-Ru(NO) was found to be a little higher than that of Ru(NO). The differences seem to stem mainly from ruthenium particle sizes and reduction behavior of adsorbed CO on the catalysts, which would be consistent with the results of CH4 formation from temperature-programmed reduction (TPR) of pre-adsorbed CO, as well as Ru particle sizes, as ascertained by H2 and CO adsorptions and TEM measurements. The Ru particle sizes of used catalysts obtained after 120h-reaction were approximately close to those of fresh catalysts and no ruthenium aggregation occurred. The origin of catalyst deactivation was investigated in terms of the extent of hydrocarbon deposition. The adsorbed atomic carbon at the peak temperature around 250–350°C was eliminated by H2 treatment, but the more heavy hydrocarbons at peak temperature over 400°C such as polymeric and graphitic carbons were not removed by any treatment. The nature of hydrocarbon deposition would be suggested by measuring the deposited carbon with the help of the characterizations, such as thermo-gravimetric analysis, temperature-programmed reduction and diffuse reflectance infrared Fourier transform (FT-IR) measurements.

Active size-controlled Ru catalysts for selective CO oxidation in H2

We propose an activation method to control Ru particle size in supported Ru catalysts, viz. commercial Ru/Al2O3 and home-made Ru/SiO2, in order to increase the catalytic activity for the preferential CO oxidation (PROX). Ru particle size is controlled by adjusting pre-treatment conditions and it affects the catalytic activity for the PROX over supported Ru catalysts. Several measurements: inductively coupled plasma-atomic emission spectroscopy (ICP-AES), bright-field transmission electron microscopy (TEM), X-ray absorption fine structure (XAFS), CO chemisorption, and O2 chemisorption were conducted to characterize the catalysts. The co-presence of H2 and O2 is essential for controlling the Ru particle size accurately. The PROX activity especially at low temperatures increases with increasing particle size of Ru, which seems to be closely related to the adsorption behavior of O2 on Ru surface.