Monometallic Ni Catalysts Research Articles

Catalytic Hydrotreatment of the Pyrolytic Sugar and Pyrolytic Lignin Fractions of Fast Pyrolysis Liquids Using Nickel Based Catalysts

Catalytic hydrotreatment is recognized as an efficient method to improve the properties of pyrolysis liquids (PO) to allow co-feeding with fossil fuels in conventional refinery units. The promising catalyst recipes identified so far are catalysts with high nickel contents (38 to 57 wt.%), promoted by Cu, Pd, Mo and/or a combination, and supported by SiO2, SiO2-ZrO2, SiO2-ZrO2-La2O3 or SiO2-Al2O3. To gain insights into the reactivity of the pyrolytic sugar (PS) and pyrolytic lignin (PL) fraction of PO, hydrotreatment studies (350 °C, 120 bar H2 pressure (RT) for 4 h) were performed in a batch autoclave. Catalyst performance was evaluated by considering the product properties (H/C ratio, the charring tendency (TGA) and molecular weight distribution (GPC)) and the results were compared with a benchmark Ru/C catalyst. All Ni based catalysts gave products oils with a higher H/C compared to Ru/C. The Mo promoted catalyst performed best, giving a product with the highest H/C ratio (1.54) and the lowest TG residue (0.8 wt.% compared to 12 wt.% for the fresh PS). The results further revealed that the PS fraction is highly reactive and full conversion was achieved at 350 °C. In contrast, the PL fraction was rather inert, and only part of the PL fraction was converted. The fresh and spent catalysts after the hydrotreatment of the PS and PL fractions were characterized by elemental analysis, powder X-Ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM-EDX). The results revealed that the use of PS as the feed leads to higher amounts of coke deposits on the catalysts, and higher levels of Ni agglomeration when compared to experiments with PL and pure PO. This proofs that proper catalyst selection for the PS fraction is of higher importance than for the PL fraction. The Mo promoted Ni catalysts showed the lowest amount of coke and the lowest tendency for Ni nanoparticle agglomeration compared to the monometallic Ni and bimetallic Ni-Cu catalysts.

Mild hydroisomerization of heavy naphtha on mono- and bi-metallic Pt and Ni catalysts supported on Beta zeolite

Abstract Hydroisomerization of long chain paraffins has emerged as a promising process for the valorization of low value fuel cuts, such as heavy naphtha, from crude oil-, coal- and bio-based feedstocks. In this study, the hydroisomerization reaction is investigated on a series of mono- and bi-metallic Pt (0.2 wt%) and/or Ni (10 wt%) catalysts supported on Beta zeolite with SiO2/Al2O3 ratio 75. Catalysts exhibit similar reactivity in the hydroisomerization of n-octane model compound, despite the very different loading and the 40% lower Bronsted acidity of the Ni-containing materials. This suggests that hydrogenation/dehydrogenation is the rate limiting step of the reaction due to very low loading of Pt and the weak dehydrogenating capacity of Ni. The latter also leads to up to 34% lower selectivity to i-C8 for the monometallic Ni catalyst. The addition of Pt in the bimetallic Ni-Pt catalyst, not only restores, but enhances the isomerization selectivity, favoring the production of di-branched to mono-branched isomers. The characterization results show that Pt enhances the reducibility and improves the dispersion of Ni, leading to increased metallic/acid sites ratio. Hydroisomerization tests with refinery naphtha as feed highlight the promising performance of this catalyst, as Ni-Pt/H-Beta increases the octane number of naphtha by 13% at mild temperature and pressure (260 °C, 10 bar), improving significantly the quality of naphtha for gasoline applications.

The synergistic effect between Ni sites and Ni-Fe alloy sites on hydrodeoxygenation of lignin-derived phenols

The catalytic hydrodeoxygenation (HDO) of lignin-derived phenolic compounds is a critical step in the upgrading of bio-oil. Here, bimetallic Ni-Fe nanoparticles supported on mesoporous carbon spheres (MCSs) were fabricated and applied in HDO of phenol. In comparison with monometallic Ni and Fe catalysts, the bimetallic Ni-Fe catalyst exhibited better performance for phenol HDO due to the formation of Ni-Fe alloy phase identified by X-ray powder diffraction (XRD) and Mössbauer spectroscopy techniques. Among several explored ratios, the catalysts with Ni/Fe ratio of 3/1 presented the highest cyclohexane yield. The reaction occurred in two consecutive steps: the hydrogenation of phenol to cyclohexanol and the further hydrogenolysis of cyclohexanol to cyclohexane. Kinetic studies showed that the hydrogenolysis of cyclohexanol controlled the overall reaction rate of phenol HDO due to the lower reaction rate of this step. Indeed, the turnover frequency (TOF) values of cyclohexanol normalized by surface metallic Ni sites exhibited a linear correlation with Ni-Fe alloy sites. The alloying of iron in the bimetallic Ni-Fe catalysts significantly enhanced the adsorption strength of cyclohexanol, which is the reason of the high activity of the Ni-Fe alloy particles. Thus, Fe-containing sites adsorb the hydroxyl species while Ni sites perform the H2 activation, their synergistic effect plays a key role in phenol HDO process.

The effect of Pt on the carbon pathways in the dry reforming of methane over Ni-Pt/Ce0.8Pr0.2O2-δ catalyst

The present work extensively discusses the carbon pathways in the dry reforming of methane with carbon dioxide (DRM) at 750 °C towards syngas (CO/H2 ˜ 1) over 5 wt% Ni, 0.5 wt% Pt and their bimetallic alloy (5 wt% Ni-0.5 wt% Pt) supported on the reducible Ce0.8Pr0.2O2-δ carrier for the first time. Various transient and isotopic experiments (use of 13CO2 and 18O2) were designed and performed aiming at providing important information about the effect of insertion of Pt in the Ni/Ce0.8Pr0.2O2-δ solid (one pot wet impregnation) on the amounts (mg gcat−1) and transient rates (μmol gcat−1 s−1) of “carbon” formation via CH4/He (methane decomposition), CO/He (reverse Boudouard reaction) and the combination of the two (CH4/CO/He). Also, the effect of Pt on the amount and transient rate of “carbon” removal via the participation of support’s mobile active oxygen species during DRM was probed. Hydrogen reduction of the Ce0.8Pr0.2O2-δ support alone at 750 °C followed by transient isothermal CO2/He treatment (750 °C) probed the existence of an alternative path of CO2 activation in the presence of support’s oxygen vacant sites. The quantification of the origin of “carbon” in the DRM (CH4 vs CO2 activation route) was performed after using isotopically labelled 13CO2 in the feed gas stream. It was found that “carbon” deposition on supported Ni and Ni-Pt alloy was largely due to the CH4 activation route on the metal surface, whereas for the supported Pt, both activation routes applied. Temperature-programmed oxidation (TPO) was used to estimate the amount and reactivity of the “carbon” deposited as a function of time-on-stream in CH4/He, CO/He, CH4/CO/He and DRM reactions. It was found that even though supported bimetallic Ni-Pt provided a small drop in CH4-conversion compared to the supported monometallic Ni catalyst, a remarkable decrease in the rate of “carbon” accumulation was obtained for the former catalyst. The latter was ∼32 times lower after 12 h in DRM (20%CH4, CO2/CH4 = 1) at 750 °C. This is largely due to the reduced rate of “carbon” deposition (via CH4 decomposition) and the enhanced rate of its gasification by lattice oxygen. The supported bimetallic Ni-Pt catalyst presented overall an excellent performance and stability after 50 h in DRM at 750 °C with a low amount of accumulated “carbon” (0.38 wt%), which is considered, to our knowledge, as one of the lowest values reported so far for bimetallic Ni-based supported catalysts.

Hydrogen Oxidation on Ni-Based Electrocatalysts: The Effect of Metal Doping

Carbon supported nanoparticles of monometallic Ni catalyst and binary Ni-Transition Metal (Ni-TM/C) electrocatalytic composites were synthesized via the chemical reduction method, where TM stands for the doping elements Fe, Co, and Cu. The chemical composition, structure and morphology of the Ni-TM/C materials were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDS). The electrochemical properties towards hydrogen oxidation reaction in alkaline medium were studied using the rotating disc electrode and cycling voltammetry methods. A significant role of the TM dopants in the promotion of the hydrogen electrooxidation kinetics of the binary Ni-TM/C materials was revealed. A record-high in exchange current density value of 0.060 mA cm2Ni was measured for Ni3Fe1/C, whereas the monometallic Ni/C counterpart has only shown 0.039 mA cm2Ni. In order to predict the feasibility of the electrocatalysts for hydrogen chemisorption, density functional theory was applied to calculate the hydrogen binding energy and hydroxide binding energy values for bare Ni and Ni3TM1.

Partial oxidation of methane over monometallic and bimetallic Ni-, Rh-, Re-based catalysts: Effects of Re addition, co-fed reactants and catalyst support

Partial oxidation reactions of CH4 over monometallic Ni, Rh, Re and bimetallic Re-Ni catalysts supported by Al2O3 were studied at 400–700 °C. Among monometallic catalysts, Rh/Al2O3 exhibited the highest catalytic activity. Lower CH4 conversion and H2 yield were observed over Ni/Al2O3 catalyst, while Re/Al2O3 catalyst did not promote the reaction under the studied condition. Addition of Re over Ni to form a bimetallic catalyst considerably promoted the activity of Ni/Al2O3 catalyst, particularly at a higher temperature (600 °C). Re-Ni proportion was then optimized; Re-Ni/Al2O3 at Re:Ni ratio of 3:7 resulted in a significantly higher CH4 conversion as well as H2 and CO yields when compared to noble-metal Rh/Al2O3 catalyst. Stability testing of Re-Ni/Al2O3, Ni/Al2O3 and Rh/Al2O3 catalysts was also conducted. After 18-h operation, Re-Ni/Al2O3 catalyst still exhibited high stability with slight deactivation in terms of H2 yield, whereas Ni/Al2O3 and Rh/Al2O3 catalysts showed higher deactivation rates. Post-reaction temperature programmed oxidation confirmed the better resistance toward carbon deposition of Re-Ni/Al2O3 catalyst. The effect of steam and CO2 addition on the Re-Ni/Al2O3 catalyst performance was also investigated. The presence of a suitable H2O content could increase H2 and CO yields and reduce the amount of carbon deposition, whereas the presence of CO2 showed undesirable influence on the reaction by reducing CH4 conversion and H2/CO ratio. Lastly, Re-Ni/Gd-CeO2 catalyst was prepared and tested to study the effect of catalyst support. The catalyst stability and resistance toward carbon deposition were significantly improved, which could be due to the high oxygen storage capacity of Gd-CeO2.

CO2 hydrogenation into CH4 over Ni–Fe catalysts

Here, we report, for the first time, on the catalytic hydrogenation of CO2 to methane at atmospheric pressure. For the preparation of hydrogenation catalysts based on Ni and Fe metals, a convenient method is developed. According to this method, low-temperature reduction of the co-precipitated Ni and Fe oxides with hydrogen gives the effective and selective bimetallic Ni[Formula: see text]Fe[Formula: see text], Ni[Formula: see text]Fe[Formula: see text] and Ni[Formula: see text]Fe[Formula: see text] catalysts. At the temperature range of 300–400[Formula: see text]C, they exhibit a high efficiency of CH4 production with respect to monometallic Ni and Fe catalysts. The results imply a synergistic effect between Ni and Fe which caused the superior activity of the Ni[Formula: see text]Fe[Formula: see text] catalyst conversing [Formula: see text]% of CO2 into CH4 at 350[Formula: see text]C. To adapt the Ni–Fe catalysts in the industry, the effect of two different carriers on the efficiency of the alumina-supported Ni[Formula: see text]Fe[Formula: see text] catalyst was investigated. It is found that the Ni[Formula: see text]Fe[Formula: see text]/[Formula: see text]-Al2O3 catalyst effectively conversed CO2 giving 100% methane yield already at 275[Formula: see text]C.

Influence of Re addition to Ni/SiO2 catalyst on the reaction network and deactivation during hydrodeoxygenation of m-cresol

The reaction network of hydrodeoxygenation of m-cresol was investigated over Ni/SiO2 and Ni-Re/SiO2 catalysts at 300 °C and 1 atm H2. m-Cresol conversion proceeds through three major primary pathways: phenyl ring hydrogenation to 3-methylcyclohexanone and 3-methylcyclohexanol, CC hydrogenolysis to CH4 and phenol, and deoxygenation to toluene. Re addition promotes dehydrogenation of the initially formed methylcyclohexanone and methylcyclohexanol to surface intermediates followed by deoxygenation toward formation of toluene. CC hydrogenolysis happens on unsaturated compounds with phenyl ring, instead of saturated compounds, since dehydrogenation is requested prior to CC cleavage. The turnover frequency (TOF) for CH4 formation follows the order of m-cresol < toluene << benzene, indicating that CC hydrogenolysis is accelerated after deoxygenation and/or demethylation. Increasing reaction temperature promotes both deoxygenation and hydrogenolysis. The toluene selectivity keeps low even at higher temperature of 340 °C on monometallic Ni catalyst due to successive CC hydrogenolysis to CH4. Re addition not only promotes deoxygenation to toluene by providing active Ni-Re neighboring sites, but also inhibits the aromatics hydrogenolysis to CH4, resulting in high toluene selectivity on bimetallic catalyst. Both catalysts show a similar deactivation trend and coke is speculated to be the major reason for deactivation.

Ni-Sn-Supported ZrO2 Catalysts Modified by Indium for Selective CO2 Hydrogenation to Methanol.

Ni and NiSn supported on zirconia (ZrO2) and on indium (In)-incorporated zirconia (InZrO2) catalysts were prepared by a wet chemical reduction route and tested for hydrogenation of CO2 to methanol in a fixed-bed isothermal flow reactor at 250 °C. The mono-metallic Ni (5%Ni/ZrO2) catalysts showed a very high selectivity for methane (99%) during CO2 hydrogenation. Introduction of Sn to this material with the following formulation 5Ni5Sn/ZrO2 (5% Ni-5% Sn/ZrO2) showed the rate of methanol formation to be 0.0417 μmol/(gcat·s) with 54% selectivity. Furthermore, the combination NiSn supported on InZrO2 (5Ni5Sn/10InZrO2) exhibited a rate of methanol formation 10 times higher than that on 5Ni/ZrO2 (0.1043 μmol/(gcat·s)) with 99% selectivity for methanol. All of these catalysts were characterized by X-ray diffraction, high-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM), X-ray photoelectron spectroscopy, CO2-temperature-programmed desorption, and density functional theory (DFT) studies. Addition of Sn to Ni catalysts resulted in the formation of a NiSn alloy. The NiSn alloy particle size was kept in the range of 10–15 nm, which was evidenced by HRTEM study. DFT analysis was carried out to identify the surface composition as well as the structural location of each element on the surface in three compositions investigated, namely, Ni28Sn27, Ni18Sn37, and Ni37Sn18 bimetallic nanoclusters, and results were in agreement with the STEM and electron energy-loss spectroscopy results. Also, the introduction of “Sn” and “In” helped improve the reducibility of Ni oxide and the basic strength of catalysts. Considerable details of the catalytic and structural properties of the Ni, NiSn, and NiSnIn catalyst systems were elucidated. These observations were decisive for achieving a highly efficient formation rate of methanol via CO2 by the H2 reduction process with high methanol selectivity.

Performance of Activated‐Carbon‐Supported Ni, Co, and Ni–Co Catalysts for Hydrogen Iodide Decomposition in a Thermochemical Water‐Splitting Sulfur–Iodine Cycle

AbstractBimetallic Ni–Co/activated carbon (Ni–Co/AC) and monometallic Ni/AC and Co/AC catalysts were prepared to investigate their catalytic activity for hydrogen‐iodide decomposition in the sulfur–iodine (SI) cycle. Transmission electron microscopy (TEM) revealed an average size of approximately 3 nm particles for Ni–Co/AC. Ni–Co/AC possesses a higher ID/IG intensity ratio in Raman spectroscopy than the monometallic catalysts and support, which is an indication of high degree of defects. Hydrogen‐iodide decomposition was performed on a fixed vertical bed quartz reactor at a weight hourly space velocity (WHSV) of 12.9 h−1 and different temperatures (400–550 °C). Bimetallic catalysts exhibited better activity and stability than the monometallic catalysts. The composition of Ni/Co in the bimetallic Ni–Co catalyst played the key role in dictating the activity of catalyst. It was observed that the loading ratio of 3:1 for Ni/Co achieved the maximal hydrogen‐iodide conversion value. Bimetallic Ni(3 %)–Co(1 %)/AC showed excellent time‐on‐stream stability of 70 h for the hydrogen‐iodide decomposition reaction. The post‐reaction characterization studies (X‐ray diffraction and Brunauer–Emmett–Teller surface area measurements) confirmed that the bimetallic Ni–Co/AC catalyst has a stable structure and shows high corrosion resistance against the corrosive hydrogen iodide environment. Also, it was observed that the apparent activation energy of the bimetallic Ni–Co/AC catalyst was smaller than the monometallic Ni and Co catalysts. The effect of iodine on hydrogen‐iodide conversion was also studied.

Effect of impregnation sequence of Mg on performance of mesoporous alumina supported Ni catalyst in dry reforming of methane

In this study, effect of Mg impregnation sequence on the activity of the mesoporous alumina supported Ni catalysts was investigated in dry reforming of methane. Characterization and activity test results showed that Mg incorporation sequence significantly influenced the physicochemical properties and the activity of the catalyst as well as coke deposition during reforming reaction. The synthesized catalysts were characterized by x-ray diffraction, N2 adsorption, temperature programmed reduction, scanning electron microscopy, CO2-temperature programmed desorption, inductively coupled plasma optical emission spectrometry, x-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy (FTIR) and pyridine adsorbed diffuse reflectance FTIR spectroscopy techniques. Mg incorporation altered the reduction profile of the monometallic catalyst and increased the reduction temperature of the nickel particles. XRD diffraction peaks corresponding to γ-A2O3 and α-Al2O3, as well as nickel-magnesium spinels and metallic Ni were observed depending on Mg incorporation sequence. The monometallic Ni catalyst showed higher activity than the bimetallic NiMg catalysts. However, coke formation was significantly influenced as a result of synthesis route. Total organic carbon, thermogravimetric analysis and SEM images exhibited that the highest coke formation was obtained over the catalyst which was prepared by sequential impregnation of Mg and then Ni. Almost no coke formation was observed on the spent catalyst, which was synthesized by simultaneously impregnation of Mg and Ni, due to the high interaction between Ni and Mg with the formation of a NiOMgO solid solution during the high calcination temperature.

Layered double hydroxide-derived Ni-Cu nanoalloy catalysts for semi-hydrogenation of alkynes: Improvement of selectivity and anti-coking ability via alloying of Ni and Cu

Environmental benign non-noble NiCu catalysts with well-distributed homogeneous nanoalloy structure was fabricated from layered double hydroxide for semi-hydrogenation of acetylene. Compared with monometallic Ni catalyst, the introduction of Cu enhanced ethene selectivity and decreased the deactivation rate in long-term reaction. Furthermore, to give a thorough understanding on structure dependent performance, conventional impregnation was also used to obtain bimetallic NiCu catalyst for comparison. Interestingly, imp-NiCu/MMO presented the mixture of monometallic Ni, Cu and bimetallic NiCu. Catalytic results indicated that 100% conversion was achieved at 160 °C with improved selectivity (>70%) over NiCu nanoalloy catalyst, while bimetallic NiCu catalyst with mixed structure showed both poor conversion (50%) and selectivity (65%). Enhanced activity was attributed to small particle size (3.2 nm) and high metal dispersion (31.4%). Improved selectivity and anti-coking ability were related to the alloying of Ni with Cu, which was conducive to isolate Ni atoms from one another confirmed by STEM-EDX and transfer electron from Cu to Ni certified by XPS. Additionally, superior performance was also found in semi-hydrogenations of hexyne, phenylacetylene, 1,2-diphenylethyne and ethyl phenylpropiolate over NiCu nanoalloy.

Effects of indium on Ni/SiO2 catalytic performance in hydrodeoxygenation of anisole as model bio-oil compound: Suppression of benzene ring hydrogenation and C–C bond hydrogenolysis

SiO2-supported monometallic Ni and bimetallic Ni-In catalysts were prepared and used for hydrodeoxygenation of anisole, which was used as a model bio-oil compound, for BTX (benzene, toluene, and xylene) production. The effects of the Ni/In ratio and Ni content on the structures and performances of the catalysts were investigated. The results show that In atoms were incorporated into the Ni metal lattice. Although the Ni-In bimetallic crystallites were similar in size to those of monometallic Ni at the same Ni content, H2 uptake by the bimetallic Ni-In catalyst was much lower than that by monometallic Ni because of dilution of Ni atoms by In atoms. Charge transfer from In to Ni was observed for the bimetallic Ni-In catalysts. All the results indicate intimate contact between Ni and In atoms, and the In atoms geometrically and electronically modified the Ni atoms. In the hydrodeoxygenation of anisole, although the activities of the Ni-In bimetallic catalysts in the conversion of anisole were lower than that of the monometallic Ni catalyst, they gave higher selectivities for BTX and cyclohexane as a result of suppression of benzene ring hydrogenation and C–C bond hydrogenolysis. They also showed lower methanation activity. These results will be useful for enhancing carbon yields and reducing H2 consumption. In addition, the lower the Ni/In ratio was, the greater was the effect of In on the catalytic performance. The selectivity for BTX was primarily determined by the Ni/In ratio and was little affected by the Ni content. We suggest that the performance of the Ni-In bimetallic catalyst can be ascribed to the geometric and electronic effects of In.

Investigation of Ni/Fe/Mg zeolite-supported catalysts in steam reforming of tar using simulated-toluene as model compound

Abstract Catalytic performance of Ni/zeolite, Ni-Fe/zeolite, and Ni-Fe-Mg/zeolite catalysts were investigated in steam reforming of toluene as a biomass tar model compound to explore promotional effect of MgO and Fe on Ni/zeolite support. The Ni-Fe-Mg/zeolite catalysts with optimum metallic composition showed higher catalytic performance over corresponding monometallic Ni and Fe catalysts and Ni-Fe/zeolite (bimetallic) catalysts. Addition of Mg to Ni-Fe/zeolite catalyst enhanced the tar reforming reactions and increased the carbon deposition tolerance. The results suggest that Ni-Fe/zeolite and Ni-Fe-Mg/zeolite catalysts have great potential for application in the steam reforming of biomass tar.

Co-production of hydrogen and carbon nanotubes from real-world waste plastics: Influence of catalyst composition and operational parameters

The use of Ni-Fe catalysts for the catalytic pyrolysis of real-world waste plastics to produce hydrogen and high value carbon nanotubes (CNT), and the influence of catalyst composition and support materials has been investigated. Experiments were conducted in a two stage fixed bed reactor, where plastics were pyrolysed in the first stage followed by reaction of the evolved volatiles over the catalyst in the second stage. Different catalyst temperatures (700, 800, 900°C) and steam to plastic ratios (0, 0.3, 1, 2.6) were explored to optimize the product hydrogen and the yield of carbon nanotubes deposited on the catalyst. The results showed that the growth of carbon nanotubes and hydrogen were highly dependent on the catalyst type and the operational parameters. Fe/γ-Al2O3 produced the highest hydrogen yield (22.9mmol H2/gplastic) and carbon nanotubes yield (195mgg−1plastic) among the monometallic catalysts, followed by Fe/α-Al2O3, Ni/γ-Al2O3 and Ni/α-Al2O3. The bimetallic Ni-Fe catalyst showed higher catalytic activity in relation to H2 yield than the monometallic Ni or Fe catalysts because of the optimum interaction between metal and support. Further investigation of the influence of steam input and catalyst temperature on product yields found that the optimum simultaneous production of CNTs (287mgg−1plastic) and hydrogen production (31.8mmol H2/gplastic) were obtained at 800°C in the absence of steam and in the presence of the bimetallic Ni-Fe/γ-Al2O3 catalyst.

Hydrogenolysis of Glycidol as an Alternative Route to Obtain 1,3‐Propanediol Selectively Using MOx‐Modified Nickel‐Copper Catalysts Supported on Acid Mesoporous Saponite

AbstractNi and Cu mono‐ and bimetallic catalysts modified with various types of acid oxides MOx (M=Mo, V, W, and Re) were tested for the hydrogenolysis of glycidol as an alternative route to the hydrogenolysis of glycerol to obtain 1,3‐propanediol (1,3‐PrD). Characterization results revealed that the presence of modifiers affected the dispersion and reducibility of the NiO particles and the strength and amount of acid sites. Among the modifiers tested, Re led to the highest activity, a high propanediols selectivity, and the highest 1,3‐PrD/1,2‐propanediol (1,2‐PrD) ratio. The Ni‐Cu/Re ratio was optimized to improve the catalytic activity. The best catalytic result, with a 46 % 1,3‐PrD yield and a 1,3‐PrD/1,2‐PrD ratio of 1.24, was obtained if the monometallic Ni catalyst at 40 wt % loading and modified with 7 wt % Re was used at 393 K and 5 MPa H2 pressure after 4 h of reaction. The overall 1,3‐PrD yield starting from glycerol and assuming a two‐step synthesis (glycerol→glycidol→1,3‐PrD) and a yield of 78 % for the first step would be 36 %. This 1,3‐PD yield is the highest for a reaction catalyzed by a non‐noble metal and is comparable to the direct hydrogenolysis of glycerol using noble metal catalysts at a longer time and a high H2 pressure.

Nanoparticles, nanosponges, methods of synthesis, and methods of use

Environmental benign non-noble NiCu catalysts with well-distributed homogeneous nanoalloy structure was fabricated from layered double hydroxide for semi-hydrogenation of acetylene. Compared with monometallic Ni catalyst, the introduction of Cu enhanced ethene selectivity and decreased the deactivation rate in long-term reaction. Furthermore, to give a thorough understanding on structure dependent performance, conventional impregnation was also used to obtain bimetallic NiCu catalyst for comparison. Interestingly, imp-NiCu/MMO presented the mixture of monometallic Ni, Cu and bimetallic NiCu. Catalytic results indicated that 100% conversion was achieved at 160 °C with improved selectivity (>70%) over NiCu nanoalloy catalyst, while bimetallic NiCu catalyst with mixed structure showed both poor conversion (50%) and selectivity (65%). Enhanced activity was attributed to small particle size (3.2 nm) and high metal dispersion (31.4%). Improved selectivity and anti-coking ability were related to the alloying of Ni with Cu, which was conducive to isolate Ni atoms from one another confirmed by STEM-EDX and transfer electron from Cu to Ni certified by XPS. Additionally, superior performance was also found in semi-hydrogenations of hexyne, phenylacetylene, 1,2-diphenylethyne and ethyl phenylpropiolate over NiCu nanoalloy.

Mono-, bi-, and tri-metallic Ni-based catalysts for the catalytic hydrotreatment of pyrolysis liquids

Catalytic hydrotreatment is a promising technology to convert pyrolysis liquids into intermediates with improved properties. Here, we report a catalyst screening study on the catalytic hydrotreatment of pyrolysis liquids using bi- and tri-metallic nickel-based catalysts in a batch autoclave (initial hydrogen pressure of 140 bar, 350 °C, 4 h). The catalysts are characterized by a high nickel metal loading (41 to 57 wt%), promoted by Cu, Pd, Mo, and/or combination thereof, in a SiO2, SiO2-ZrO2, or SiO2-Al2O3 matrix. The hydrotreatment results were compared with a benchmark Ru/C catalyst. The results revealed that the monometallic Ni catalyst is the least active and that particularly the use of Mo as the promoter is favored when considering activity and product properties. For Mo promotion, a product oil with improved properties viz. the highest H/C molar ratio and the lowest coking tendency was obtained. A drawback when using Mo as the promoter is the relatively high methane yield, which is close to that for Ru/C. 1H, 13C-NMR, heteronuclear single quantum coherence (HSQC), and two-dimensional gas chromatography (GC × GC) of the product oils reveal that representative component classes of the sugar fraction of pyrolysis liquids like carbonyl compounds (aldehydes and ketones and carbohydrates) are converted to a large extent. The pyrolytic lignin fraction is less reactive, though some degree of hydrocracking is observed.

Cooperativity and Dynamics Increase the Performance of NiFe Dry Reforming Catalysts.

The dry reforming of methane (DRM), i.e., the reaction of methane and CO2 to form a synthesis gas, converts two major greenhouse gases into a useful chemical feedstock. In this work, we probe the effect and role of Fe in bimetallic NiFe dry reforming catalysts. To this end, monometallic Ni, Fe, and bimetallic Ni-Fe catalysts supported on a MgxAlyOz matrix derived via a hydrotalcite-like precursor were synthesized. Importantly, the textural features of the catalysts, i.e., the specific surface area (172-178 m2/gcat), pore volume (0.51-0.66 cm3/gcat), and particle size (5.4-5.8 nm) were kept constant. Bimetallic, Ni4Fe1 with Ni/(Ni + Fe) = 0.8, showed the highest activity and stability, whereas rapid deactivation and a low catalytic activity were observed for monometallic Ni and Fe catalysts, respectively. XRD, Raman, TPO, and TEM analysis confirmed that the deactivation of monometallic Ni catalysts was in large due to the formation of graphitic carbon. The promoting effect of Fe in bimetallic Ni-Fe was elucidated by combining operando XRD and XAS analyses and energy-dispersive X-ray spectroscopy complemented with density functional theory calculations. Under dry reforming conditions, Fe is oxidized partially to FeO leading to a partial dealloying and formation of a Ni-richer NiFe alloy. Fe migrates leading to the formation of FeO preferentially at the surface. Experiments in an inert helium atmosphere confirm that FeO reacts via a redox mechanism with carbon deposits forming CO, whereby the reduced Fe restores the original Ni-Fe alloy. Owing to the high activity of the material and the absence of any XRD signature of FeO, it is very likely that FeO is formed as small domains of a few atom layer thickness covering a fraction of the surface of the Ni-rich particles, ensuring a close proximity of the carbon removal (FeO) and methane activation (Ni) sites.

Understanding the Performance and Stability of Supported Ni-Co-Based Catalysts in Phenol HDO

Performances of bimetallic catalysts (Ni-Co) supported on different acidic carriers (HZSM-5, HBeta, HY, ZrO2) and corresponding monometallic Ni catalysts in aqueous phase hydrodeoxygenation of phenol were compared in batch and continuous flow modes. The results revealed that the support acidity plays an important role in deoxygenation as it mainly controls the oxygen-removing steps in the reaction network. At the same time, sufficient hydrothermal stability of a solid catalyst is essential. Batch experiments revealed 10Ni10Co/HZSM-5 to be the best-performing catalyst in terms of conversion and cyclohexane yield. Complementary continuous runs provided more insights into the relationship between catalyst structure, efficiency and stability. After 24 h on-stream, the catalyst still reveals 100% conversion and a slight loss (from 100% to 90%) in liquid hydrocarbon selectivity. The observed alloy of Co with Ni increased dispersion and stability of Ni-active sites, and combination with HZSM-5 resulted in a well-balanced ratio of metal and acid sites which promoted all necessary steps in preferred pathways. This was proved by studies of fresh and spent catalysts using various characterization techniques (N2 physisorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and infrared spectroscopy of adsorbed pyridine (pyr-IR)).