Metallic Nickel Species Research Articles

Alloying nickel with phosphorus to switch the selective conversion of furfural from furans to cyclopentanones or 1,4-pentanediol

Metallic nickel species generally show high activity for hydrogenation of C=C in furfural, eliminating the formation of furfuryl alcohol (FA) that is the precursor for production of value-added chemical such as 1,4-pentanediol (1,4-PeD) and cyclopentanone (CPO). To tackle this issue, alloying of nickel in Ni/SiO2 catalyst with phosphorus for suppressing the excessive hydrogenation activity was conducted in this study. The results showed that the increase of phosphorus loading led to the transition of the alloy phase from Ni12P5 to Ni3P and then to Ni2P, which was also accompanied with the increased abundance and strength of Lewis acid sites but not the Brønsted acid sites. The acidic sites constructed by P-O structure (phosphates) can effectively adsorb C-O of furfural, preventing the transformation of the adsorption to vertical configuration and facilitated the ring-opening and rearrangement of furfural to CPO and 1.4-PeD. Selective conversion of furfural to 1,4-PeD with the yield of 85.3 % could be achieved over Ni-10 %P/SiO2 catalyst but only at 150 °C with the aid of the Lewis acidic sites while not the Brønsted acid sites. The conversion of furfural at 170 °C over Ni-15 %P/SiO2 catalyst activated Brønsted acid sites and hydrogenation sites for catalyzing formation of CPO and cyclopentanol (CPL) with sum yield of up to 93.6 %. The selective conversion of furfural to either 1,4-PeD or CPO thus could be flexibly switched by tailoring activity of the acid sites and hydrogenation sites.

Impacts of temperature on hydrophilicity/functionalities of char and evolution of bio-oil/gas in pyrolysis of pig manure

Pig manure is a carbonaceous waste and has a distinct composition with biomass and the pyrolysis products properties could also be different. In this study, particular attention was paid on the evolution of functionalities and the changes of hydrophobicity/hydrophilicity of char with an increase in temperature, as these surface properties determine the applications of char as support of catalyst or adsorbent. Our results demonstrated that both oxygen and nitrogen-containing organic species in manure were thermally unstable, decomposition of which initiated from 200 °C and proceeded to near completion at 600 °C. The substantial deoxygenation at 300–500 °C did not result in the proportional increase of carbon content of char, as the carbonization did not take place effectively. Instead, the excessive cracking of these organic species made the inorganic SiO2 and CaCO3 as the dominant species in the char formed at high temperatures. The abundant oxygen-containing functionalities in the char produced via pyrolysis below 300 °C could not be sufficiently exposed, leading to the high hydrophobicity of char. In comparison, the exposure of the inorganic species in the char produced at high pyrolysis temperature made char more hydrophilic, which, however, was not favorable for the dispersion of metallic nickel species in the Ni/char catalyst.

Correlations of Lewis acidic sites of nickel catalysts with the properties of the coke formed in steam reforming of acetic acid

Coking is a major challenge in the reactions of steam reforming. In addition to the nature of metal species, the properties of carrier also affect coking behaviors of a reforming catalyst. In this work, we prepared nickel carried on Al2O3, SiO2 or the molecular sieves (25-H, 38-H) for assessed in steam reforming of acetic acid. The Ni/Al2O3 catalyst contained abundant Lewis acidic sites while the Ni/SiO2, Ni/38-H and Ni/25-H catalysts did not. The Lewis acidic sites in Ni/Al2O3 induced the polymerisation reactions to form the polymeric coke, which wrapped metallic nickel species and was the primary reason for deactivation of catalyst, even though the amount of coke was small. The substantial amount of coke formed over the other three catalysts did not lead to rapid catalyst deactivation. With the form of carbon nanotube or other forms was mainly the type of catalytic coke, depending on characteristic of the carrier. Comparing with the polymeric coke in the catalyst of Ni/Al2O3, the catalytic coke had a high C/H ratio, a much higher thermal stability and was more aromatic rich.

Impacts of metal loading in Ni/attapulgite on distribution of the alkalinity sites and reaction intermediates in CO2 methanation reaction

Both metal sites and alkaline sites are essential parameters for a catalyst used in methanation of CO2. This study investigated the impacts of the relative abundance of metal sites and alkaline sites on the catalytic performances of nickel-based catalyst with attapulgite, a natural mineral, as the support. The results showed that the increase of nickel loading to attapulgite significantly decreased the abundance of alkaline sites, remarkably enhanced the catalytic activity, and suppressed the formation of CO. The in situ DRIFTS characterization of the CO2 methanation indicated that the alkaline sites favored formation of the oxygen-containing reaction intermediates such as CO∗, –OH, ∗CO2, formate, carbonate and bicarbonate species. In comparison, metallic nickel species promoted their further hydrogenation to form CH4. Besides the absorption/activation of ∗CO2 was more preferable on surface of metallic nickel, but not on the alkaline sites. The availability of the alkaline sites was not as important as the metallic nickel species for preparation of an efficient catalyst for CO2 methanation.

Impacts of nickel loading on properties, catalytic behaviors of Ni/γ–Al2O3 catalysts and the reaction intermediates formed in methanation of CO2

In this study, methanation of CO2 over Ni/Al2O3 with varied nickel loading (from 0 to 50 wt%) was evaluated, striving to explore the effects of nickel loading on catalytic behaviors and the reaction intermediates formed. The results showed that agglomeration of nickel particles were closely related to interaction between nickel and alumina. Increasing nickel loading resulted in the increased proportion of nickel having medium strong interaction with alumina, the reduced reduction degree of NiO, the increase of medium to strong basic sites, the enhanced activity for methanation and the competition between reverse water gas shift (RWGS) reaction and methanation. Lower nickel loading promoted RWGS reaction while methanation of CO2 dominated at higher nickel loading. The catalyst with a nickel loading around 25% achieved the best activity for methanation. The in–situ DRIFTS studies of methanation of CO2 showed that CO2 could be absorbed on surface of metallic Ni, NiO or alumina. More metallic nickel species on alumina suppressed formation of carbonate species while promoted further conversion of HCOO∗ species and ∗CH3 species, achieving a higher catalytic efficiency. Moreover, more metallic nickel species was crucial for gasifying the carbonaceous intermediates, prevented aggregation of the intermediates to coke and achieving a higher catalytic stability.

Synergistic Effect of Oxygen Vacancies and Ni Species on Tuning Selectivity of Ni/ZrO₂ Catalyst for Hydrogenation of Maleic Anhydride into Succinic Anhydride and γ-Butyrolacetone.

ZrO2 nanoparticles, ZrO2 (P) and ZrO2 (H), with different tetragonal phase contents, were prepared. ZrO2 (P) possessed higher tetragonal phase content than ZrO2 (H). Ni/ZrO2 catalysts (10% (w/w)), using ZrO2 (P) and ZrO2 (H) as supports, were prepared using an impregnation method, and were characterized using XRD, Raman, H2-TPR, XPS, and H2-TPD techniques. Their catalytic performance in maleic anhydride hydrogenation was tested. The Ni/ZrO2 (P) catalyst exhibited stronger metal-support interactions than the Ni/ZrO2 (H) catalyst because of its higher number of oxygen vacancies and the low-coordinated oxygen ions on its surface. Consequently, smaller Ni crystallites and a higher C=C hydrogenation activity for maleic anhydride to succinic anhydride were obtained over a Ni/ZrO2 (P) catalyst. However, the C=O hydrogenation activity of Ni/ZrO2 (P) catalyst was much lower than that of the Ni/ZrO2 (H) catalyst. A 43.5% yield of γ-butyrolacetone was obtained over the Ni/ZrO2 (H) catalyst at 210 °C and 5 MPa of H2 pressure, while the yield of γ-butyrolactone was only 2.8% over the Ni/ZrO2 (P) catalyst under the same reaction conditions. In situ FT-IR characterization demonstrated that the high C=O hydrogenation activity for the Ni/ZrO2 (H) catalyst could be attributed to the surface synergy between active metallic nickel species and relatively electron-deficient oxygen vacancies.

Study of LaxNiOy and LaxNiOy/MgAl2O4 catalysts in dry reforming of methane

Bulk LaxNiOy and supported LaxNiOy/MgAl2O4 (with x=1 or 2 and y=3 or 4) catalysts have been prepared respectively by sol-gel and impregnation methods The elaborated materials have been characterized by XRD, BET, H2-TPR, H2-chemisorption and TPO. The catalytic activity was evaluated in dry reforming of methane (DMR) with an equimolar ratio of CH4 and CO2. XRD analysis shows the presence of LaNiO3, La2NiO4 and MgAl2O4 phases. Higher specific surface areas and nickel dispersions were obtained for the supported catalysts. H2-TPR analysis revealed a low reducibility of the nickel in the supported solids. Supported catalysts were found more active and stable than bulk one in DMR in good agreement with higher Ni dispersion and the beneficial role of the basic support. The XRD analysis performed on the spent catalysts (after 65h of catalytic test) revealed the presence of the initial phases with metallic nickel species. The TPO analysis showed a low carbon deposition for the supported catalysts. A kinetic study based on the reaction mechanism points out the participation of the reverse water gas shift reaction (RWGS) for the conversion of CO2 and of the produced H2 as well as contribution of steam methane reforming reaction for the conversion of CH4, with water produced from (RWGS), for temperatures over 1023K.

HDO activity of carbon-supported Rh, Ni and Mo-Ni catalysts

This work reports the performance of low metal loading (about 3wt.%) Rh, Ni and Mo-Ni catalysts supported on carbon in the hydrodeoxygenation (HDO) of phenol. The catalytic tests were carried out in a flow microreactor at 310°C and at a total hydrogen pressure of 3MPa. A commercial NiMoP/γ-Al2O3 sulfided catalyst was used as reference. The effect of catalyst pre-treatment (reduction against sulfidation) was investigated in the case of the noble metal catalyst. The thermally treated in inert atmosphere, fresh reduced and spent catalysts have been characterized by several physicochemical techniques: chemical analysis, N2 adsorption-desorption isotherms, Raman spectroscopy, Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and High Resolution Transmission Electron Microscopy (HRTEM).The HDO of phenol was found to be favored on the bifunctional Rh/C and Ni/AC catalysts which exhibit a large amount of well dispersed metallic species (from HRTEM). Contrary to a commercial sulfided NiMo/Al2O3 catalyst, the hydrogenation of aromatic ring of phenol was favored being the CO bond hydrogenolysis a minor reaction route. Catalytic HDO of phenol over Rh/C reveal that the catalyst activation by reduction is advantageous compared to that by sulfidation. The partial substitution of Ni by Mo in the Mo-Ni/AC catalyst led to enhance of the catalyst stability but decrease of overall activity occurs due to the decrease of amount of metallic nickel species. The role of the MoO3 species in the inhibition of deactivation by coke is discussed.

Effects of Nickel Species on Ni/Al2O3 Catalysts in Carbon Nanotube and Hydrogen Production by Waste Plastic Gasification: Bench- and Pilot-Scale Tests

Upcycling waste plastics into carbon nanotubes (CNTs) and hydrogen is attractive for its efficient disposal. Although Ni-based catalysts are typically used in both hydrogen production and CNT synthesis, few studies have investigated the catalytic active site for the co-production of CNTs and hydrogen by waste plastic gasification. To evaluate the effect of nickel species distribution of the Ni/Al2O3 catalyst, it was prepared by an impregnation method using different calcination atmospheres to determine their feasibility for the co-production of CNTs and hydrogen. For comparison, various Ni/Al2O3 catalysts for CNT growth were examined by CH4 thermal chemical vapor deposition (CVD). Ni/Al2O3 calcined under a reductive H2 atmosphere (H–Ni/Al2O3) gave smaller nickel nanoparticles containing metallic nickel species, which showed optimal performance for CNT and hydrogen co-production by waste plastic gasification. In addition, the quality of the CNTs was higher using this process compared to the CNTs synthesize...

In situ synthesis of nickel carbide-promoted nickel/carbon nanofibers nanocomposite catalysts for catalytic applications

In the present work, nickel carbide-promoted nickel/carbon nanofibers nanocomposite catalysts (NiC-Ni/CNFs) were directly in situ generated by a facile catalytic chemical vapor deposition (CCVD). The materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The results showed that carbon supported nickel catalysts (Ni/C) could catalyze the growth of CNFs in CCVD, while nickel carbides were formed simultaneously under acetylene atmosphere and further successfully stabilized by uniform CNFs to form NiC-Ni/CNFs. This applied method did not need the pretreatment of multiple steps including the purification of CNFs and subsequent immobilization of active metallic nickel species. As-formed NiC-Ni/CNFs catalysts exhibited excellent performance in liquid phase selective hydrogenation of o-chloronitrobenzene to o-chloroaniline with a high yield of 96.6%, which was mainly attributed to a synergistic catalytic effect between metallic nickel and nickel carbide species. Furthermore, such nickel carbide-promoted Ni-based catalyst showed excellent catalytic performance in the selective hydrogenations of p- and m-chloronitrobenzenes to p- and m-chloroaniline.

Hydrogen production from oxidative reforming of methane on Ni/γ-Al2O3 catalysts: Effect of support promotion with La, La–Ce and La–Zr

Ni/Al2O3 catalysts promoted by adding La2O3, La2O3–CeO2 and La2O3–ZrO2 were investigated on oxidative and steam reforming aiming the hydrogen production. The samples were characterized by surface area estimation (BET), XRD, TPR, TPD-H2 and XANES. Analysis of TEM and TPO was performed as complementary characterization for catalysts after reaction. The oxidative steam reforming of methane at temperatures above 500°C reveals that all the promoted catalysts presented better activities than the unpromoted. Below 500°C, the catalysts presented deactivation due to metallic nickel species oxidation and the TEM analysis of Ni/Al and Ni/La–Al catalysts revealed that the lanthanum addition led to a decrease in the Ni species particle size and also to a better active phase dispersion. The results suggest that below 500°C the activity may be related to differences in the metallic area values, although the Ni/La2O3–Al2O3 catalysts have shown a different behavior.

Promoting Effect of Sulfur Addition on the Catalytic Performance of Ni/MgAl2O4 Catalysts for Isobutane Dehydrogenation

Ni/MgAl2O4 catalysts with high NiO loadings were highly active for isobutane cracking, which led to abundant formation of methane, hydrogen and coke. The results of activity testing and XRD characterization jointly revealed that large ensembles of metallic nickel species formed during reaction notably catalyzed cracking instead of dehydrogenation. However, after introduction of sulfur into Ni/MgAl2O4 catalyst through impregnation with ammonium sulfate, undesired cracking reactions were effectively inhibited, and the selectivity to isobutene increased remarkably. Totally, up to ∼42 wt % isobutene could be obtained at 560 °C in a single pass after the modification. From the characterization results, it was also concluded that, after sulfur introduction, NiO particles became much smaller and better dispersed on the catalyst surface. NiS species, formed during the induction period of the reaction, not only facilitated isobutene desorption from the catalyst, but also constituted the active sites for isobutane ...

Coke- and sintering-resistant monolithic catalysts derived from in situ supported hydrotalcite-like films on Al wires for dry reforming of methane

Monolithic catalysts derived from in situ supported hydrotalcite-like films on Al wires display high resistance to coke formation and sintering in the dry reforming of methane due to their hierarchical porous structure, well dispersed metallic nickel species, more basic sites and strong metal-support interaction effect.

Synthesis gas production in the combined CO2 reforming with partial oxidation of methane over Ce-promoted Ni/SiO2 catalysts

A series of nickel-based catalyst supported on silica (Ni/SiO2) with different loading of Ce/Ni (molar ratio ranging from 0.17 to 0.84) were prepared using conventional co-impregnation method and were applied to synthesis gas production in the combination of CO2 reforming with partial oxidation of methane. Among the cerium-containing catalysts, the cerium-rich ones exhibited the higher activity and stability than the cerium-low ones. The temperature-programmed reduction (TPR) and UV–vis diffuse reflectance spectroscopy (UV–vis DRS) analysis revealed that the addition of CeO2 reduced the chemical interaction between Ni and support, resulting in an increase in reducibility and dispersion of Ni. Over NiCe-x/SiO2 (x = 0.17, 0.50, 0.67, 0.84) catalysts, the reduction peak in TPR profiles shifted to the higher temperature with increasing Ce/Ni molar ratio, which was attributed to the smaller metallic nickel size of the reduced catalysts. The transmission electron microscopy (TEM) and X-ray diffraction (XRD) for the post-reaction catalysts confirmed that the promoter retained the metallic nickel species and prevented the metal particle growth at high reaction temperature. The NiCe-0.84/SiO2 catalyst with small Ni particle size exhibited the stable activity with the constant H2/CO molar ratio of 1.2 during 6-h reaction in the combination of CO2 reforming with partial oxidation of methane at 850 °C and atmospheric pressure.

Reconstruction of historical exposures in the US nickel alloy industry and the implications for carcinogenic hazard and risk assessments

Recently, various regulatory authorities have been reexamining the potential carcinogenic hazards and risks associated with exposures to nickel and certain nickel compounds. In making their assessments, the authorities have focused on occupational cohorts at facilities where nickel-containing sulfidic ores were processed and where increased lung and nasal cancer risks were found in specific groups of workers. Little attention, however, has been paid to the vast number of workers in nickel-using industries, where no excess respiratory cancer risks have been observed. In this paper, the historical exposures of one such group of workers engaged in the production of nickel alloys are reconstructed, and the implications for cancer risk assessments are analyzed. The results indicate that nickel alloy workers were exposed to insoluble oxidic and metallic nickel species at levels comparable to those found in certain nickel processing cohorts; yet they experienced no increase in respiratory cancer risks. This suggests that extrapolating risks from certain primary nickel producers to other nickel industry sectors may not be appropriate.

Use of a non-thermal plasma for the production of synthesis gas from biogas

Abstract The conversion of biogas (mixture CH 4 /CO 2 : 60/40) was studied using pulsed dielectric barrier discharges at different temperatures. The influence of the presence of a catalyst obtained after reduction of the perovskite LaNiO 3 was reported. The main products of the reaction were hydrogen and carbon monoxide, but hydrocarbons such as: C 2 H 6 , C 2 H 4 , C 2 H 2 , C 3 H 8 , trace amounts of C4 to C6, and oxygenate compounds: methanol, ethanol, and acetone, were also formed.The conversion increased with the temperature, the selectivity of light hydrocarbons (C 2 , C 3 , and C 4 ) is maximum at 673 K. When the temperature is higher than 673 K, CO production is favoured resulting most probably from the reaction between deposited carbon and an active oxygen species. The results showed that the plasma catalyst association facilitates the CO 2 activation and influences the product selectivities. It is possible to admit that the metallic nickel species react as “radicals trap”, while the basicity of the La 2 O 3 favours the activation of CO 2 increasing the CO selectivity as soon as discharge plasma are combined with the catalyst.

Catalytic Behavior of Supported KNiCa Catalyst and Mechanistic Consideration for Carbon Dioxide Reforming of Methane

Carbon dioxide reforming of methane to synthesis gas has been investigated using a KNiCa catalyst loaded on a highly siliceous NaZSM-5 zeolite support which was promoted with alumina. The catalytic behavior of the supported KNiCa catalyst has also been compared to that of the supported Ni catalyst. Long-time catalytic measurements at 800°C show that the supported KNiCa catalyst has excellent catalyst stability for 140 h due to the promotional effect of surface carbonate species leading to surface enrichment of carbon dioxide, while the supported Ni catalyst is subjected to severe catalyst deactivation due to extensive coke deposition less than 40 h on stream. Pulse reaction, thermogravimetric analysis, isotope experiment, and X-ray absorption spectroscopy have been performed for understanding the detailed chemistry and the mechanistic aspects of the CO2 reforming. Pulse reaction and thermogravimetric analysis on the supported KNiCa catalyst indicate that methane is activated on the surface Ni species and carbon dioxide interacts with alkaline promoters to form surface carbonates which hinder the formation of inactive coke or scavenge carbon from the surface Ni species. A study of deuterium isotope effects for the reforming reaction shows that there is almost no isotope effect on the supported KNiCa catalyst, suggesting that a CH4 dissociation step is not rate determining. In this work, mechanistic investgations reveal that reaction between the adsorbed carbon species and the dissociated oxygen atoms on Ni sites of catalyst surface leads to the production of carbon monoxide and the regeneration of metallic nickel species as a consequence, which is assumed to be a rate-determining step in the CO2 reforming. It is also proposed that the oxidation step of surface carbon with surface oxygen or adsorbed CO2 as surface carbonate species on the catalyst is important for maintaining catalyst stability of the supported KNiCa by the efficient removal of surface carbon species.

Catalytic hydrogenation of carbon dioxide over LaNi 5 activated during the reaction

The hydrogenation of carbon dioxide to methane can be catalyzed over an intermetallic compound of LaNi 5 at 250–350°C. The catalytic activity at 250°C increases during the reaction while X-ray diffraction (XRD) analyses show that the structure of the compound decomposes to La(OH) 3, LaCO 3OH, and metallic nickel. Formation of metallic nickel species during the reaction also takes place in a nickel–lanthanum oxides catalyst prepared by a coprecipitation method, however, the activity is not so high as the former catalyst. Surface analyses by X-ray photoelectron spectroscopy (XPS) suggest that new nickel species interacting with lanthanum cation, possibly Ni–O–La, are formed in LaNi 5 during the reaction, and the species are supposed to be rather active than metallic nickel.