Ni Surface Area Research Articles

Vapour Phase Hydrogenation of Cinnamaldehyde over Ni/γ-Al2O3 Catalysts: Interesting Reaction Network

The vapour phase hydrogenation of cinnamaldehyde over Ni loading γ-Al2O3 catalysts was performed at 1 atm and 300 °C in a fixed-bed reactor. The major product was hydrocinnamaldehyde. Unexpected products of styrene and ethylbenzene due to new reaction pathway of hydrodeformylation were observed. The results indicated that Ni metal was the active centers and the catalytic activity was parallel to the Ni surface area. The stability of TOF values implied that the cinnamaldehyde hydrogenation over Ni/γ-Al2O3 catalysts was a structure insensitive reaction.

High performance sorbents for diesel oil desulfurization

Sorbents with different Ni loading supported on silica–alumina (SiAl) and activated carbon (AC) were synthesized and tested for removal of sulfur compounds from a model diesel oil, containing nearly 250 ppmw S as benzothiophene (BT), dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT). A state-of-art Commercial Ni-based sorbent and two Norit activated carbons were also tested for comparison. Moreover, the influence on sorbents uptake capacity of the presence of aromatics in amounts representative of real diesel oils was studied. Both commercial and home-made materials performed worse in presence of aromatic compounds. Probably, the latter competed with the refractory sulfur compounds (DBT and 4,6-DMDBT) in the adsorption on active sites. As a first important result of the investigation the sorbents carrying 45% and 30% of Ni on SiAl showed a breakthrough uptake capacity of nearly, respectively, 2 and 2.6 times higher than Commercial sorbent as a consequence of their higher Ni dispersion and surface area. Moreover, activated carbons and the sample with 28%Ni on AC showed an even higher breakthrough uptake capacities. In particular, the deposition of nickel on activated carbon is an innovative approach which takes advantage of the selectivity of Ni towards S-species and the high adsorptive capacity of AC support.

Effect of hydrogen sulfide on the direct internal reforming of methane in solid oxide fuel cells

Electrochemical full cell evaluation of a Versa Power Systems TSC-2 solid oxide fuel cell was conducted in 1 ppmv hydrogen sulfide (H2S) at 750 °C with 25%, 35% and 50% levels of direct internal reforming (DIR) of methane. It is shown that the addition of H2S significantly degrades both the cell voltage as well as the DIR activity of the cell, as evidenced by gas chromatographic analysis of the cell exhaust gas. With the removal of H2S, the cell voltage recovers, but not to pre-H2S exposure levels. The onset of degradation of electrochemical activity commences before the onset of DIR activity degradation, indicating that H2S penetrates to the Ni-containing anode functional layer before saturation coverage of Ni with sulfur in the support layer. Secondary ion mass spectrometric post-analysis indicated that, while adsorbed sulfur remains on the surface of Ni after recovery for ∼200 h in H2S-free gas, there remains sufficient active Ni surface area in the anode substrate to continue to catalyze the DIR reactions.

Catalytic modification of Ni–Sm-doped ceria anodes with copper for direct utilization of dry methane in low-temperature solid oxide fuel cells

A Cu/Ni/Sm-doped ceria (SDC) anode has been designed for direct utilization of dry methane in low-temperature anode-supported solid oxide fuel cells. The anode is prepared by the impregnation method, whereby a small amount of Cu is incorporated into the previously prepared Ni/SDC porous matrix. After reduction, Cu nanoparticles adhere to and are uniformly distributed on the surface of the Ni/SDC matrix. For the resulting Cu/Ni/SDC anode-supported cell, maximum power density of 317mWcm−2 is achieved at 600°C. The power density shows only ∼2% loss after 12-h operation. The results demonstrate that the Cu/Ni/SDC anode effectively suppresses carbon deposition by decreasing the Ni surface area available and the level of carbon monoxide disproportionation. This combination of effects results in very low-power density loss over the operating time.

C9-aldehyde hydrogenation over nickel/kieselguhr catalysts in trickle bed reactor

Abstract The objective of the present study was to select the optimal catalyst and operating conditions for the manufacture of C 9 -alcohol, using C 9 -aldehyde and hydrogen, in a trickle bed reactor. When CaO, Ce 2 O 3 or MgO was added as a promoter to the Ni/kieselguhr catalyst, the BET and Ni surface areas were increased. In the reaction for the manufacture of C 9 -alcohol, using C 9 -aldehyde and hydrogen in a batch reactor, a Ni–MgO/kieselguhr catalyst showed the highest activity. In addition, the catalyst using Na 2 CO 3 as a precipitant showed the highest activity. According to the result of an experiment to find the optimal reaction conditions for C 9 -alcohol synthesis, using C 9 -aldehyde and hydrogen in a trickle bed reactor loaded with Ni–MgO/kieselguhr catalyst, the highest yield of C 9 -alcohol was 91.5 wt% at 130 °C, 400 psi and WHSV = 3. The C 9 -aldehyde hydrogenation performance of the Ni–MgO/kieselguhr catalyst was similar to that of a Cu/ZnO/Al 2 O 3 catalyst, but superior to that of Cu–Ni–Cr–Na/Al 2 O 3 and Ni–Mo/Al 2 O 3 catalysts. In a long-term catalysis test, the Ni–MgO/kieselguhr catalyst showed higher stability than the Cu/ZnO/Al 2 O 3 catalyst.

Steam reforming of ethanol on Ni–CeO2–ZrO2 catalysts: Effect of doping with copper, cobalt and calcium

Steam reforming (SR) and oxidative steam reforming (OSR) of ethanol were investigated over undoped and Cu, Co and Ca doped Ni/CeO2–ZrO2 catalyst in the temperature range of 400–650 °C. The nickel loading was kept fixed at 30 wt.% and the loading of Cu and Co was varied from 2 to 10 wt% whereas the Ca loading was varied from 5 to 15 wt.%. The catalysts were characterized by various techniques, such as surface area, temperature programmed reduction, X-Ray diffraction and H2 chemisorption. For Cu and Co doped catalyst, CuO and Co3O4 phases were detected at high loading whereas for Ca doped catalyst, no separate phase of CaO was found. The reducibility and the metal support interactions were different for doped catalysts and varied with the amount and nature of dopants. The hydrogen uptake, nickel dispersion and nickel surface area was reduced with the metal loading and for the Co loaded catalysts the dispersion of Ni and nickel surface area was very low. For Cu and Ca doped catalysts, the activity was increased significantly and the main products were H2, CO, CH4 and CO2. However, the Co doped catalysts showed poor activity and a relatively large amount of C2H4, C2H6, CH3CHO and CH3COCH3 were obtained. For SR, the maximum enhancement in catalytic activity was obtained with in the order of NCu5. For Cu–Ni catalysts, CH3CHO decomposition and reforming reaction was faster than ethanol dehydrogenation reaction. Addition of Cu and Ca enhanced the water gas shift (WGS) and acetaldehyde reforming reactions, as a result the selectivity to CO2 and H2 were increased and the selectivity to CH3CHO was reduced significantly. The maximum hydrogen selectivity was obtained for Catalyst N (93.4%) at 650 °C whereas nearly the same selectivity to hydrogen (89%) was obtained for NCa10 catalyst at 550 °C. In OSR, the catalytic activity was in the order N > NCu5 > NCa15 > NCo5. In the presence of oxygen, oxidation of ethanol was appreciable together with ethanol dehydrogenation. For SR reaction, the highest hydrogen yield was obtained on the undoped catalyst at 600 °C. However, with calcium doping the hydrogen yields are higher than the undoped catalyst in the temperature range of 400–550 °C.

Sintering of nickel catalysts: Effects of time, atmosphere, temperature, nickel-carrier interactions, and dopants

Supported nickel catalysts are widely used in the steam-reforming process for industrial scale production of hydrogen and synthesis gas. This paper provides a study of sintering in nickel-based catalysts (Ni/Al 2O 3 and Ni/MgAl 2O 4). Specifically the influence of time, temperature, atmosphere, nickel-carrier interactions and dopants on the rate of sintering is considered. To probe the sintering kinetics, all catalysts were analyzed by sulfur chemisorption to determine the Ni surface area. Furthermore selected samples were further analyzed using X-ray diffraction (XRD), mercury porosimetry, BET area measurements, and electron microscopy (EM). The observed sintering rates as a function of time, temperature, and P H 2 O / P H 2 ratio were consistent with recent model predictions [J. Sehested, J.A.P. Gelten, I.N. Remediakis, H. Bengaard, J.K. Nørskov, J. Catal. 223 (2004) 432] over a broad range of environmental conditions. However, exposing the catalysts to severe sintering conditions the loss of nickel surface area is faster than model predictions and the deviation is attributed to a change in the sintering mechanism and nickel removal by nickel-carrier interactions. Surprisingly, alumina-supported Ni particles grow to sizes larger than the particle size of the carrier indicating that the pore diameter does not represent an upper limit for Ni particle growth. The effects of potassium promotion and sulfur poisoning on the rates of sintering were also investigated. No significant effects of the dopants were observed after ageing at ambient pressure. However, at high pressures of steam and hydrogen (31 bar and H 2O:H 2 = 10:1) potassium promotion increased the sintering rate relative to that of the unpromoted catalyst. Sulfur also enhances the rate of sintering at high pressures, but the effect of sulfur is less than for potassium.

Liquid-phase Reductive Deposition as Novel Preparation Method for Highly Dispersive Nickel Catalysts

We have been developing the selective deposition method onto TiO2 nanoparticles, named as the liquid-phase selective-deposition method, where TiO2 plays a role of formation center of Ni nanoparticles as well as protection from the aggregative growth of the particles. The concept of this method is to well disperse and stabilize Ni nanoparticles on TiO2 surface by specific adsorption of Ni precursory complexes and then heterogeneous nucleation on the adsorption sites. The particle size was decreased with increasing the amount of Zn added, thus the catalytically active Ni surface area was increased. The selective deposition onto TiO2 surface and addition of Zn to the nanoparticle promoted the catalytic activity of Ni–Zn nanoparticle, e.g. the catalytic activity of Ni–Zn/TiO2 was ca. 10 times higher than that of the unsupported Ni nanoparticles. Ni in the nanocomposite was assigned as metallic, although their surface was oxidized under the atmospheric condition, but Zn and B were deposited as their oxide.

CO and CH4 Electrochemical Oxidation on Ni Patterned Anodes

Single cell SOFCs with Ni patterned anodes sputtered onto single crystal YSZ electrolyte discs were used to examine electrochemical oxidation of H 2 , CO, and CH 4 under dry and wet (∼4% H 2 O) conditions. High-surface-area porous YSZ/LSM cathodes provided low cathodic overpotentials for isolation of anodic processes. Polarization curves of H 2 and CO from 750-850°C indicated that for patterns with < 100 μm line widths, power densities and impedance spectra more closely scale with Ni surface area than with three-phase-boundary lengths. CH 4 electrochemical oxidation also suggested a very weak influence of three-phase boundary lengths for temperature ≥ 800°C. Results indicate detrimental effects of H 2 O on CO oxidation power densities due to drops in open-circuit voltages, although polarization resistances did not drop significantly. Similar drops in OCV with H 2 O addition were observed for CH4, but steam-reforming rates become significant above 800°C such that polarization resistances for CH 4 increase to approach those of H 2 . Impedance spectra suggest that a Jow frequency process controls CO oxidation for temperatures ≤ 800°C but becomes less dominant at higher temperatures. Impedance spectra for CH 4 oxidation show the dramatic drop in polarization resistance as steam-reforming rates become appreciable, indicating the importance of temperature in sustaining reliable Ni anode performance.

Carbon dioxide reforming of methane over co-precipitated Ni–CeO 2, Ni–ZrO 2 and Ni–Ce–ZrO 2 catalysts

A co-precipitation method was employed to prepare nickel oxide dispersed on CeO 2, ZrO 2 and cubic Ce 0.8Zr 0.2O 2 support to obtain catalysts useful for carbon dioxide reforming of methane reaction. The Ni–CeO 2 and Ni–Ce–ZrO 2 catalysts showed relatively high activity and stability, while the Ni–ZrO 2 catalyst deactivated in the initial stage of the reaction due to serious carbon formation. The co-precipitated Ni–Ce–ZrO 2 catalyst exhibited the highest catalytic activity (CH 4 conversion >97% at 800 °C) among the catalysts tested and the activity was maintained without significant loss during the reaction for 100 h. The enhanced catalytic activity and stability of the co-precipitated Ni–Ce–ZrO 2 catalyst is attributed to the combination of nano-crystalline nature of cubic Ce 0.8Zr 0.2O 2 support and finely dispersed nano-sized NiO x crystallites resulting in intimate contact between Ni and support, better Ni dispersion, higher Ni surface area and enhanced oxygen transfer during the reaction.

Characterization of the Ni-Zn/TiO&lt;SUB&gt;2&lt;/SUB&gt; Nanocomposite Synthesized by the Liquid-Phase Selective-Deposition Method

The characterization of Ni-Zn/TiO 2 nanocomposite synthesized by the liquid-phase selective-deposition method was studied. Nanoparticles were well dispersed and stabilized by the selective deposition onto TiO 2 surface. The particle size was decreased with increasing the amount of Zn added, thus the catalytically active Ni surface area was increased. The selective deposition onto TiO 2 surface and addition of Zn to the nanoparticles promoted the catalytic activity of Ni-Zn nanoparticles, e.g. the catalytic activity of Ni-Zn/TiO 2 for 1-octene hydrogenation was ca. 10 times higher than that of the unsupported Ni nanoparticles. Ni in the nanocomposite was assigned as metallic, although their surface was oxidized under the atmospheric condition, but Zn and B were deposited as their oxide.

Ni/SiO 2 prepared by sol–gel process using citric acid

A Ni/SiO 2 with high Ni content over 50 wt% in NiO form was prepared from a solution of TEOS, nickel nitrate and citric acid. The additive citric acid contributes both the formation of mesopores and increase in the Ni dispersion. The Ni/SiO 2 has large mesopores with size of 5–10 nm. The mesopores are formed by eliminating citric acid from the silica–Ni–citric acid composite with small shrinkage, i.e. the spaces occupied with citric acid in the composite directly turn to pores after elimination. Although large shrinkage in pores occurs when the composite is calcined in air, the calcination in an inert atmosphere is effective to suppress the shrinkage during calcination. In addition to the controlled large mesopores, high Ni dispersion is achieved in the Ni/SiO 2. Nickel citrate formed in the as-prepared silica–Ni–citric acid composite effectively suppresses the aggregation of Ni species during drying because of low crystallization ability of nickel citrate. Furthermore, the following calcination in an inert atmosphere has an additional effect to increase Ni dispersion. Thus prepared samples keep small Ni particle size even at high Ni content of ≈50 wt% after reduction at 500 °C, and show high Ni surface area over 30 m 2 g −1.

Influence of lanthanide oxides on the catalytic activity of nickel

The catalytic activity of supported Ni/Ln 2O 3 (Ln=La, Ce, Gd, Ho, Yb) catalysts for the hydrogen/water isotopic exchange reaction has been studied. The metallic and total surface areas were measured by hydrogen and krypton adsorption, respectively. The Ni surface area evaluated by hydrogen chemisorption is higher than the total BET surface area for Ni/La 2O 3. The Ni surface area does not change significantly while the total surface area increases with the decreasing Ln 3+ ionic radius. The thermodesorption spectra for the adsorbed hydrogen with and without preadsorbed H 2O are reported. The mobility of the adsorbed hydrogen decreases from La 2O 3 to Yb 2O 3 as support and in the same direction decreases the water uptake normalised to the total surface area. The catalytic activity normalised to the Ni surface area decreases exponentially with the decreasing Ln 3+ ionic radii from La 2O 3 to Yb 2O 3 as support, in close relationship with the basicity and hydration degree of the support oxide.

Structural and Catalytic Properties of Ni/SiO2 Prepared by Solution Exchange of Wet Silica Gel

Structural formation of Ni/SiO2 in a solution exchange method, where Ni was supported on silica by exchanging the solution in wet silica gel derived from tetraethoxysilane under acidic conditions, and its catalytic property were investigated. In the preparation of Ni/SiO2, the dispersion of Ni is largely dominated by aggregation in drying, while mesopore structure in the silica support can be controlled to ∼4 nm by exchanging the solution with strong acids. When aqueous nickel nitrate solution is used in the solution exchange, large nickel nitrate crystals are formed within the gel matrix during drying. They decompose into aggregates of NiO crystallites, with sea–island distribution during calcination. On the other hand, the use of citric acid together with nickel nitrate in the solution exchange effectively inhibits the aggregation of Ni species in drying through the formation of nickel citrate, which barely crystalizes in drying. In calcination, the nickel citrates decompose into NiO particles, and their distribution in the silica matrix becomes homogeneous. Additionally, the use of citric acid and calcination in an inert atmosphere has another effect, decreasing the particle size of NiO and Ni. Consequently, we can prepare Ni/SiO2 catalyst with high Ni surface area at high Ni content, which shows superior catalytic activity in the hydrogenation of benzene.

Methane reforming over Ni/Ce-ZrO 2 catalysts: effect of nickel content

The effect of Ni content on the Ni/Ce-ZrO 2 catalyst has been investigated in the methane conversion reactions to syngas, such as oxy-reforming, steam reforming and oxy-steam reforming. Among the catalysts examined, Ni/Ce-ZrO 2 catalyst with 15% Ni loading exhibits not only the highest catalytic activity and selectivity but also remarkable stability. The TPR results reveal that strong interaction between support and metal exists and that some part of NiO incorporates into the surface of the Ce-ZrO 2 support. Combined with H 2 chemisorption results, one may deduce that Ni surface area and the chemical environment of nickel, as well as the properties of the Ce-ZrO 2 support, play very important roles in the catalytic activity and stability of Ni/Ce-ZrO 2 catalysts. It seems that two kinds of active sites, i.e. one for methane and the other for steam or oxygen, are well-balanced on 15% Ni/Ce-ZrO 2 catalyst.

Sintering of Nickel Steam-Reforming Catalysts on MgAl2O4 Spinel Supports

Sintering significantly contributes to the deactivation of Ni-based steam-reforming catalysts. We have investigated the effect of Ni loading and surface area of the support on sintering of Ni particles on MgAl2O4 spinel supports. The experiments were performed under simulated industrial pre-reforming conditions, i.e., in a 10:1 mixture of steam and hydrogen at 500°C and 30 bar total pressure. The Ni particle size of fresh and sintered catalysts was determined from sulfur chemisorption capacity, X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning transmission electron microscopy (STEM). It was found that most of the sintering occurs in the first 200 h; after that period the Ni particle size changes only slightly. A remarkable result is that the average Ni particle size after sintering reaches a limiting value that depends only weakly on the Ni loading and surface area of the support. Sintering of the catalysts with a lower Ni loading is slower and they exhibit a greater loss in Ni surface area compared to those with a higher Ni loading. Because the sintered particles are polycrystalline agglomerates, the XRD estimates of particle size are lower than those obtained by the other techniques such as TEM or chemisorption. The particle size distributions derived from TEM and STEM follow a log normal distribution, suggesting that sintering occurs through crystallite migration and coalescence. The limiting size of the Ni particles after sintering, and the low sintering rate after 200 h, can both be related to the lower mobility of the larger Ni particles on the support.

Mass-Transfer Limitation in Mesopores of Ni–MgO Catalyst in Liquid-Phase Hydrogenation

Liquid-phase hydrogenation of cyclohexanone, acetone, 2-butanone, 3-pentanone, and 4-heptanone to the corresponding secondary alcohols was investigated over various porous Ni catalysts at 0°C under a hydrogen pressure of 1.1 MPa. Pore size distributions as well as Ni surface area of Ni–MgO catalysts, which were prepared from a melt of the corresponding nitrates and citric acid, with high Ni contents of 60–80 wt% were controlled by the calcination temperature of the precursors. For the hydrogenation of acetone, reaction rate constants were directly proportional to the Ni surface areas of the catalysts, and Raney nickel which had the largest Ni surface area showed the highest reaction rate. For the hydro genation of other reactants larger than acetone in molecular size, however, rate constants do not have a simple linear correlation with Ni surface area. Ni–MgO catalysts with large mesopores exhibited reaction rates higher than those of Raney nickel catalysts with the largest Ni surface areas. Assuming that diffusion of both reactants and products is restricted in small pores such as in Raney nickel, we tried to evaluate an effective pore size for the liquid-phase mass transfer in porous materials by a novel approach analyzing reaction rate data coupled with pore size distribution and hydrogen chemisorption data. Cumulative Ni surface areas were calculated by multiplying the Ni surface area by a fraction of cumulative surface area located in pores larger than a specific size to the total surface area, and relationship between the cumulative Ni surface areas and the reaction rate constants were examined. It was found that the rate constants for the hydrogenation of 2-butanone, cyclohexanone, 3-pentanone, and 4-heptanone were proportional to cumulative Ni surface areas in pores larger than critical sizes of 2.0, 2.3, 3.2, and 3.7 nm in radius, respectively. It has been consequently elucidated that the mass transfer of the reactants is restricted in pores smaller than a critical size that depends on the size of the reactants.

Dispersion Control of Ni Particles in Porous Silica by Solution Exchange of Wet Silica Gel

Abstract Particle size of NiO in silica with well defined mesoporous structure can be controlled from 3.5 to 10 nm regardless of NiO content up to 30 wt% by solution exchange of wet silica gel derived from sol-gel process. Ni surface area of samples reduced at 500 °C can be enlarged by decreasing the NiO particle size, resulting in 30 m2g−1 at 30 wt% loading. The catalysts showed superior activities for gas-phase hydrogenation of benzene.

Deterioration Mechanism of Direct Internal Reforming Catalyst.

The deterioration mechanism of reforming catalysts used for internal reforming molten carbonate fuel cells is studied through post-test analyses of the used catalysts. The catalysts studied are Ni/MgO-Al2O3. Deactivation of the catalysts is caused both by a decrease in Ni surface area of the catalyst and by loss of specific activity of the Ni surface (alkali poisoning). The decrease in Ni surface area is characterized firstly by accelerated sintering of Ni particles due to the existence of alkali metals (attached electrolyte). Secondly, sulfur poisoning also plays an important role, especially for sintered catalysts with small Ni surface areas. As for the effect of alkali poisoning, the specific activity of the Ni surface decreases to 15–60% of the original one. Blockage of pore structure by the electrolyte does not seem to be important for the loss of Ni surface area.

Reactivity of Ni on oxygen-covered W(110) surfaces

The adsorption at 90 K of hydrogen, carbon monoxide, and benzene on Nin/O0.5/W(110) (with n=1–10) has been studied by thermal desorption, x-ray photoemission spectroscopy, ultraviolet photoemission spectroscopy, low-energy electron diffraction, and work function measurements. The surfaces are relatively inert to hydrogen adsorption, with estimated quasisaturation uptake being H/W=0.18 for n=1 and increasing to 0.36 for n=10. In contrast, CO and C6H6 adsorb readily on Ni1/O0.5/W(110), with saturation coverages of CO/W=0.85±0.09 and C6H6/W=0.18±0.03, respectively. These values are comparable to coverages obtainable on clean W(110), namely, CO/W=0.70 and C6H6/W=0.18. Coadsorption of Ni and O on W(110) and subsequent annealing to 500–1000 K leads to segregation of Ni and O, with the formation of Ni crystallites largely 〈111〉 oriented along the surface normal. The heights of these Ni ‘‘towers’’ can be adjusted by varying the amounts of coadsorbed oxygen and Ni. The Ni crystallites resist sintering, even when annealed at 1000 K for 3600 s. Adsorption of H2 and CO on them at 90 K was also investigated, and found to be less than expected from the estimated overall Ni surface area.