SiO2-supported Nickel Research Articles

How does the SiO2-supported nickel catalyst improve the ethylene polymerization process? Insights from DFT studies

Polymerization of ethylene plays a pivotal role in the production of polyethylene, a widely used polymer. Efficient catalysts are crucial for enhancing the polymerization process and improving polymer properties. In this study, we employ density functional theory (DFT) calculations to investigate the influence of the SiO2 surface by linker approach on the reactivity of ethylene polymerization catalyzed by the Ni-α-imine ketone-type complex. Our results unveil valuable insights into molecular interactions and mechanistic aspects driving the improved polymerization process in good agreement with experimental findings. We identify strong hydrogen bonds as the key factor facilitating the favorable binding of the molecular catalyst with the SiO2 surface, involving a chemisorption process. Furthermore, we find that chain initiation is a rate-determining step for the molecular catalyst, whereas chain propagation is rate-determining for the supported catalyst, aligning with experimental differences in ethylene polymerization activity. Energy decomposition analysis reveals the dominant roles of electrostatic and orbital interactions in stabilizing both catalysts. Notably, the chemisorbed catalyst exhibits enhanced catalyst-ethylene interaction, while steric effects primarily impact the reactivity of the homogeneous catalyst. The supported catalyst exhibits a higher propagation barrier due to a late transition state. Additionally, the heterogeneous catalyst demonstrates superior ethylene uptake and thermal stability across a range of temperatures in agreement with the experimental data. These findings offer guidance for future experimental designs, emphasizing the importance of heterogenization and catalyst-ethylene interaction for enhancing ethylene polymerization processes.

Flow synthesis of N-alkyl-5-methyl-2-pyrrolidones over Ni2P/SiO2 catalyst

N-alkyl-5-methyl-2-pyrrolidones are an attractive alternative to the common solvent N-methyl-2-pyrrolidone (NMP) and can be used as starting materials for synthesis of various valuable chemicals. Reductive amination of alkyl levulinates derived from biomass feedstock is a promising method for production of these compounds. In the present work, N-alkyl-5-methyl-2-pyrrolidones were obtained in excellent yields by reductive amination of ethyl levulinate with alkylamines over SiO2-supported nickel phosphide in a flow reactor using molecular hydrogen as a reducing agent. At the same time, aromatic amines and 1-nitropropane give a lower yield of the corresponding pyrrolidones. The influence of the solvent nature, temperature, pressure, hydrogen and liquid flow rates on the catalyst performance was studied.

Benefits of the SiO2-supported nickel phosphide catalyst on ethylene oligomerization

Although homogeneous catalytic systems have been central in ethylene oligomerization, the SiO2-Al2O3-supported nickel phosphide (Ni2P) catalyst was recently examined to be capable of transforming ethylene into higher olefins. Herein, better catalytic performance in ethylene oligomerization is achieved with Ni2P/SiO2 than Ni2P/SiO2-Al2O3 and Ni2P/Al2O3. As a factor influencing ethylene oligomerization, the particle size of Ni2P is the smallest over Ni2P/SiO2 due to strong metal-support interaction. While the oligomer productivity is affected by the density of Brønsted acid site present in the supported Ni2P catalysts, Ni2P/SiO2 has a relatively high ratio of Brønsted to Lewis acid sites. Moreover, Ni2P/SiO2 is able to easily generate and transfer hydrogen species via the Brønsted acid POH groups, which would affect formation of nickel hydride species that is important in oligomerizing ethylene. Therefore, the above features of Ni2P/SiO2 are beneficial for ethylene oligomerization into higher olefins.

Oxidative degradation of cresol isomers using ozone in the presence of SiO2-supported nickel, iron, manganese and vanadium catalysts

We report the catalytic ozonation as a viable tool in the oxidative degradation of cresol isomers. SiO2-supported metal catalysts with 2.5 and 7.5 wt.% (Ni, Fe, Mn, V) were employed in this ozone initiated oxidation reactions. All catalysts were characterized using various analytical techniques such as XRD, FT-IR, SEM-EDX, TEM, ICP-OES, and BET-surface area analyses. XRD studies revealed the existence of Fe as Fe2O3 and Mn as Mn3O4 on the supports’ surface. EDX results displayed a dispersion homogeneity of the metals over the surface of SiO2 support, and the ICP-OES analysis confirm the concentration of a loaded metal. The degradation of cresols (m-, o-, p-cresol) was investigated by aerating each substrate with ozone (0.123 mg/L) in a glass reactor from 6 to 24 h of reaction time at ambient reaction conditions. The catalytic activities of various metal loaded SiO2 catalysts in terms of conversion and selectivity were studied. The reaction products of various cresol isomers were identified using GC–MS analysis. m-Tolyl acetate (m-TA), 2,3-dihydroxytoluene (2,3-DT), diethyl maleate (DM) and diethyl oxalate (DO) were the identified products in the oxidative degradation of m-Cresol. Whereas, o-cresol yielded o-tolyl acetate (o-TA), 2,5-dihydroxytoluene (2,5-DT), DM and DO as products. p-Cresol produced p-tolyl acetate (p-TA), 3,4-dihydroxytoluene (3,4-DT), DM and DO as reaction products. The Ni(2.5%)/SiO2 catalyst possess excellent activity towards the conversion of m-cresol (85.0%), whereas, Fe(2.5%)/SiO2 led to highest conversion for both o-cresol (76.3%) and p-cresol (87.0%).

Low-Temperature Catalytic CO2 Dry Reforming of Methane on Ni-Si/ZrO2 Catalyst

The activity of a ZrO2-supported nickel catalyst promoted by silica (Ni-Si/ZrO2) in CO2 dry reforming of methane was carried out at 400 and 450 °C. The catalysts were prepared by an impregnation method and characterized by H2-TPR, XRD, TEM, TG-MS, Raman, XPS, and in situ XPS and DRIFTS. It was discovered that Ni-Si/ZrO2 showed higher initial conversion of CH4 (0.50 s–1) and CO2 (0.44 s–1), and stability for low temperature (400 °C) DRM reaction in comparison to an SiO2-supported nickel catalyst promoted by zirconia (Ni-Zr/SiO2) (0.32 s–1 for both CO2 and CH4). The Ni-Si/ZrO2 catalyst featured the formation of active nickel particles with a small size of 6–9 nm and with slightly strong electronic donor ability, stabilization of the initial metal nickel state under the reaction conditions, and the formation of easily removed C1 coke. However, for the 450 °C DRM reaction, the coke that formed on the Ni-Si/ZrO2 catalyst was mainly C2 coke that was difficult to remove, because the CO2 preferred to combine with...

Hydrodeoxygenation of phenolic compounds to cycloalkanes over supported nickel phosphides

SiO2, HZSM-5 and Al2O3 were used to support nickel phosphides to prepare hydrodeoxygenation (HDO) catalysts. The nickel loading was kept at 20 wt% while the Ni/P molar ratio was varied among 3, 2, and 1 in the preparation by incipient wetness impregnation. XRD characterization revealed that Ni3P, Ni12P5, and Ni2P as the major crystal phases were obtained at Ni/P ratio of 3, 2, and 1, respectively, on SiO2 and HZSM-5. When Al2O3 was used as the support, nickel metal rather than nickel phosphides was generated. Among SiO2-supported nickel phosphides, Ni3P exhibited highest hydrogenation activity and catalytic performance in phenol HDO. Ni3P/HZSM-5 showed the high catalytic performance in HDO of phenol as well as catechol and o-cresol, with Ni3P as the hydrogenation site and the acid sites in HZSM-5 zeolite as the dehydration site. The strong acidity in HZSM-5 also facilitated the isomerization of cycloalkanes at elevated temperatures.

Effects of calcination and reduction temperature on the properties of Ni-P/SiO2 and Ni-P/Al2O3 and their hydrodenitrogenation performance.

A series of SiO2-supported and γ-Al2O3-supported nickel phosphides were prepared by temperature-programmed reduction (TPR) with different calcination and reduction temperatures. The prepared catalysts were characterized by XRD, BET, H2-TPR, CO titration and HRTEM. The crystal phase and CO uptake content were influenced by calcination and reduction temperature. The catalytic performance of various catalysts was tested in quinoline hydrodenitrogenation and exhibited considerable differences. The quinoline HDN activity of SiO2-supported nickel phosphides decreases with increase of calcination and reduction temperature. In contrast to SiO2-supported samples, the ability to remove nitrogen of γ-Al2O3-supported samples increases with reduction temperature.

Isobutane oxydehydrogenation on SiO 2-supported nickel molybdate catalysts: Effect of the active phase loading

The oxidative dehydrogenation of isobutane over SiO 2-supported and unsupported NiMoO 4 was studied under steady state conditions and the effect of active phase loading analysed. The SiO 2-supported catalysts were prepared by direct precipitation of NiMoO 4 on the support and characterised by BET, X-ray diffraction and temperature-programmed desorption of NH 3. Used catalysts were characterised by thermal analysis. Results show that, in SiO 2-supported catalysts, β-NiMoO 4 is stabilised even at room temperature. The SiO 2-supported NiMoO 4 catalyst with lower contents of active phase (13% NiMoO 4/SiO 2 and 26% NiMoO 4/SiO 2) present higher amount of β phase and less acidic surfaces. Besides isobutene, the reaction of isobutane over the prepared catalysts leads to the formation of CO 2, CO, light alkanes and coke. Unsupported NiMoO 4 leads to much higher amounts of total oxidation products and coke than the supported catalysts. The catalyst containing the highest amounts of β-phase (26% NiMoO 4/SiO 2) leads to higher selectivity to isobutene.

Oxidative Dehydrogenation of Isobutane on SiO2-Supported Nickel Molybdate Catalysts: Effect of the Active Phase Loading

Oxidative Dehydrogenation of Isobutane on SiO2-Supported Nickel Molybdate Catalysts: Effect of the Active Phase Loading

Characterisation of SiO2-supported nickel catalysts for carbon dioxide reforming of methane

The CO2–methane reformation reaction over Ni/SiO2 catalysts has been extensively studied using a range of temperature-programmed techniques and characterisation of the catalysts by thermogravimetry (TG), X-ray diffraction (XRD) and electron microscopy (TEM). The results indicate a strong correlation between the microstructure of the catalyst and its performance. The role of both CO2 and CH4 in the reaction has been investigated and the role of methyl radicals in the reaction mechanism highlighted. A reaction mechanism involving dissociatively adsorbed CO2 and methyl radicals has been proposed.

97/01086 Mechanism of methane partial oxidation over SiO 2-supported nickel catalyst

97/01086 Mechanism of methane partial oxidation over SiO 2-supported nickel catalyst

Pulse study of methane partial oxidation to syngas over SiO2-supported nickel catalysts

The reaction behaviors of CH4/O2 (2/1) with unreduced and reduced SiO2-supported nickel (10 wt% metal) catalysts were investigated in a pulse micro-reactor at temperatures ranging from 600 to 800° C. In the interaction of CH4/O2 with unreduced NiO/SiO2, the products are exclusively CO2 and H2O at or below 700°C. At 800° C, besides CO2 and H2O, CO and H2 are formed. The reactivity at 800°C can be ascribed to the net generation of metallic nickel site at this temperature. In the reaction of CH4/O2 over reduced Ni/SiO2, the main products are CO and H2 with CO2 and H2O being the minor ones. The results indicate metallic nickel is the active site for methane partial oxidation to syngas. Normal deuterium isotope effects of similar magnitude were observed on the overall, as well as on the CO and CO2 formation reactions with insignificant change in the product selectivities when CD4 was used instead of CH4, indicating that methane dissociation is a key step and that CO and CO2 are formed via some common intermediates which are subject to kinetic deuterium isotope effect. The results of deuterium isotope effects can be reasonably explained based on the methane pyrolysis mechanism.

Mechanistic Studies of CH4/O2Conversion over SiO2-Supported Nickel and Copper Catalysts

Methane utilization as received much attention in the past few years. Besides the methane oxidative coupling process, the partial oxidation of methane to syngas is another route being considered. In this note, the authors report the reaction behaviors of CH{sub 4} and CH{sub 4}/O{sub 2} with reduced and unreduced SiO{sub 2}-supported copper and nickel (10 wt% metal) catalysts in a pulse microreactor at 600, 650, and 700{degrees}C. 18 refs., 5 figs.

CH4/CD4 isotope effects in the carbon dioxide reforming of methane to syngas over SiO2-supported nickel catalysts

By performing the CH4 + CO2 and CD4 + CO2 reactions alternately over SiO2-supported nickel catalysts in a pulse micro-reactor, normal deuterium isotope effects on both the methane conversion reaction and on the CO formation reaction have been observed in the process of CO2 reforming of methane. Based on the observed CH4/CD4 isotope effects, the pathways for the formation of CO are discussed.