Hydrodeoxygenation Of Stearic Acid Research Articles

Construction of Metal/Zeolite Hybrid Nanoframe Reactors via in-Situ-Kinetics Transformations.

Metal/zeolite hybrid nanoframes featuring highly accessible compartmental environments, abundant heterogeneous interfaces, and diverse chemical compositions are expected to possess significant potential for heterogeneous catalysis, yet their general synthetic methodology has not yet been established. In this study, we developed a two-step in-situ-kinetics transformation approach to prepare metal/ZSM-5 hybrid nanoframes with exceptionally open nanostructures, tunable metal compositions, and abundant accessible active sites. Initially, the process involved the formation of single-crystalline ZSM-5 nanoframes through an anisotropic etching and recrystallization kinetic transformation process. Subsequently, through an in situ reaction of the Ni2+ ions and the silica species etched from ZSM-5 nanoframes, layered nickel silicate emerged on both the inner and outer surfaces of the zeolite nanoframes. Upon reduction under a hydrogen atmosphere, well-dispersed Ni nanoparticles were produced and immobilized onto the ZSM-5 nanoframes. Strikingly, this strategy can be extended to immobilize a variety of ultrasmall monometallic and bimetallic alloy nanoparticles on zeolite nanoframes. Benefiting from the structural and compositional advantages, the resultant hybrid nanoframes with a high loading of discrete Ni nanoparticles exhibited enhanced performance in the hydrodeoxygenation of stearic acid into liquid fuels. Overall, the methodology shares fresh insights into the rational construction of intricate frame-like metal/zeolite hybrid nanoreactors for many potential catalytic applications.

The critical role of solvent polarity in the preparation of tube-like Co–Mo sulfide catalysts for the hydrodeoxygenation of stearic acid

Co–Mo sulfides with tube-like structures were prepared through a low-temperature pre-sulfurization process using rod-like CoMoO4 as the precursor.

Hydrodeoxygenation of stearic acid over zeolite–MOF composite-supported Pt catalysts

Herein, we report the synthesis of a series of zeolite-porous metal–organic framework (MOF) (ZM) composites with different Pt loadings via a two-step approach, in which –COOH functionalized ZSM-5 particles were added during the formation of MIL-100(Fe) (Materials Institute Lavoisier) by a microwave-assisted solvothermal method. The acidity of the ZM composites was significantly improved compared to that of the parent materials, and the highest acidity was observed for the ZM2-based catalyst. This ZM composite-supported Pt (Pt/ZM) catalyst was investigated as a promising candidate for the selective hydrodeoxygenation (HDO) of stearic acid as a fatty acid model compound. The effect of zeolite/MOF ratio and Pt content on the catalytic behavior was also evaluated. As a result, the 3% Pt/ZM2 catalyst showed a conversion efficiency of 92% for the stearic acid HDO with a hydrocarbon selectivity of 10–11 times higher than that of the original Pt/MIL-100 (Fe). In addition, 3% Pt/ZM2 catalyst exhibited stable catalytic performance for stearic acid HDO during the recycle runs. The optimized Pt/ZM catalyst showed high thermal and catalytic stability, as well as high product yield.

Hydrodeoxygenation of stearic acid to produce diesel–like hydrocarbons: kinetic modeling, parameter estimation and simulation

• Different assumptions for the adsorption step were tested to develop a suitable kinetic model for the hydrodeoxygenation of stearic acid. • Reaction rates constants, equilibrium adsorption constants and activation energies were estimated. • The model based on non-dissociate H 2 and single-site adsorption provided the best fitting quality. • The Peng-Robinson equation of state had better performance than the Predictive-Soave-Redlich-Kwong equation to calculate hydrogen solubilities in the reaction mixture. There has been an increasing search for renewable sources to produce alternative biofuels due to the growth in the global energy demand and the environmental impacts caused by fossil fuels. Green diesel obtained via hydrotreatment of vegetable oils and fats is a promising option, mainly due to the possibility of being integrated into an existing refinery. Here, we investigate the kinetics of hydrodeoxygenation of stearic acid as a model compound of triglyceride raw materials over NiMo/Al 2 O 3 catalyst to obtain hydrocarbons in the diesel range. Kinetic models based on different assumptions to the adsorption step, such as Eley–Rideal and Langmuir–Hinshelwood mechanisms, were evaluated through nonlinear regression to parameter estimation using a hybrid algorithm combining Particle Swarm Optimization and Nelder–Mead method. All proposed models fitted well to the experimental data, presenting correlation coefficients higher than 90% for the fatty acid and the final hydrocarbons. However, the surface reaction limited model based on competitive adsorption with non-dissociate H 2 adsorbed showed the best results and was used to simulate the process.

The role of catalyst poisons during hydrodeoxygenation of renewable oils

Hydrodeoxygenation (HDO) activity of NiMo catalysts have been evaluated in the presence of catalyst poisons in bio-based feedstocks. An in-house synthesized NiMo/Al2O3 catalyst was placed in a refinery unit for biofuel production. Iron (Fe), phosphorus (P) and metals were identified as major contaminants. Calcination treatment was explored to recover the activity of spent catalysts. The effect of Fe, K and phospholipid containing P and Na on catalyst deactivation during hydrodeoxygenation of stearic acid was simulated at lab-scale. Fe caused the most deactivation where the highest feed concentration of the Fe compound resulted in 1480 ppm Fe deposited on the catalyst. Elemental distribution along the radial axis of spent catalysts indicated: Fe deposited only to a depth of 100 μm irrespective of concentration while P and Na from phospholipid and K penetrated deeper in catalyst particles with a distribution profile that was found to be concentration dependent.

Enhancement of fatty acids hydrodeoxygenation selectivity to diesel-range alkanes over the supported Ni-MoOx catalyst and elucidation of the active phase

Metal oxide modified nickel catalysts are highly desirable for the conversion of biomass-derived compounds to biofuels and valuable chemicals because of their low-cost and unique synergistic effects in catalytic reaction. Herein, a series of metal oxide modified nickel catalysts were scrutinized in the hydrodeoxygenation of steatic acid to diesel-range alkanes without any carbon loss as a model reaction. The results showed that MoOx modified Ni/SiO2 catalyst was the most active and selective for the hydrodeoxygenation of stearic acid under mild reaction conditions (260 °C and 3.0 MPa H2 partial pressure). The catalyst with an Ni/Mo molar ratio of 1, and that was reduced at an optimized temperature (500 °C), exhibited the best performance; this catalyst achieved a high selectivity (>95%) to diesel-range alkanes at 100% stearic acid conversion. A high selectivity (>60%) to C18 alkane and a less than 30% selectivity to C17 alkane were observed at 260 °C and 3.0 MPa H2 partial pressure. By selecting an appropriate support, the selectivity to C18 alkane can reach 95% at 100% stearic acid conversion over Ni–Mo/H-ZSM-5 catalysts. In contrast to Ni/SiO2, Ni–Mo/SiO2 was more efficient for CO hydrogenation and less active for C–C bond cleavage, which afforded a higher selectivity to long-chain hydrocarbons without any carbon loss. Detailed characterization, control experiments, and kinetic studies indicate that the high activity and selectivity to the C18 alkane arises from a synergy between Ni and MoOx. The Ni sites at the interface between the Ni metal and MoOx species play a role in the generation of hydride (Hδ−) species from H2 dissociation, and MoOx plays a role in promotion of fatty acids adsorption through adsorbing carboxylic groups at the oxygen vacancy of MoOx. The deep understanding of such synergic catalysis will provide significant clues for the rational design of bimetallic catalysts towards the production of diesel-range alkanes without any carbon loss from the hydrodeoxygenation of fatty acids/esters.

Studies on Nickel-based Bimetallic Catalysts for the Hydrodeoxygenation of Stearic Acid

Fatty acids, which are contained in vegetable oils, can be converted into alkanes through the hydrodeoxygenation (HDO) reaction, as an alternative fuel. In this study, the HDO of stearic acid was carried out in the presence of nickel-based bimetallic catalysts supported on Silica-Alumina (SiAl) in an autoclave batch reactor using decane as a solvent. Various metals, including Fe, Cu, and Co, were added into Ni catalysts using conventional wet impregnation method. Among others, additional Cu on Ni/SiAl increased the performance of the catalyst for the reaction.

Hydrodeoxygenation of stearic acid using Mo modified Ni and Co/alumina catalysts: Effect of calcination temperature

The calcination temperature (Cal-Temp) plays a vital role in the performance of supported metal catalysts. In this work, the alumina supported Ni, NiMo, Co, and CoMo catalysts were prepared at different Cal-Temp. The catalysts were characterized by various techniques to identify the catalytically active different surface species to correlate their role in the hydrodeoxygenation of stearic acid. With increasing Cal-Temp, the metal dispersion was increased for Ni, NiMo, and CoMo catalyst (up to 973 K) and decreased for Co catalyst. With increasing Cal-Temp, the catalytic activity was thus increased for Ni and NiMo catalyst and decreased for Co catalyst. The activity of CoMo catalyst was, however, enhanced with rising Cal-Temp up to 973 K and declined slightly after that. The optimum Cal-Temp for Ni, NiMo, Co, and CoMo catalyst was found to be 1023 K, 973 K, 773 K, and 973 K. The reaction followed the decarbonylation route over active metallic centers (Ni and Co) and the HDO route over oxophilic M2+⋅MoO2 (M = Ni/Co) and reducible cobalt oxide species. The C17 alkane was thus the principal product over Ni catalyst, whereas C18 alkane was the primary product over CoMo and NiMo catalyst. In contrast, both C17 and C18 alkanes were significant over Co catalyst.

Activated Carbon, Carbon Nanofibers and Carbon-Covered Alumina as Support for W2C in Stearic Acid Hydrodeoxygenation

Carbon materials play a crucial role in sorbents and heterogeneous catalysis and are widely used as catalyst support for several reactions. This paper reports on an investigation of tungsten carbide (W2C) catalyst on three types of carbon support, namely activated carbon (AC), carbon nanofibers (CNF) and carbon-covered alumina (CCA). We evaluated their activity and selectivity in stearic acid hydrodeoxygenation at 350 °C and 30 bar H2. Although all three W2C catalysts displayed similar intrinsic catalytic activities, the support did influence product distribution. At low conversions (<5%), W2C/AC yielded the highest amount of oxygenates relative to W2C/CNF and W2C/CCA. This suggests that the conversion of oxygenates into hydrocarbons is more difficult over W2C/AC than over W2C/CNF and W2C/CCA, which we relate to the lower acidity and smaller pore size of W2C/AC. The support also had an influence on the C18-unsaturated/C18-saturated ratio. At conversions below 30%, W2C/CNF presented the highest C18-unsaturated/C18-saturated ratio in product distribution, which we attribute to the higher mesopore volume of CNF. However, at higher conversions (>50%), W2C/CCA presented the highest C18-unsaturated/C18-saturated ratio in product distribution, which appears to be linked to W2C/CCA having the highest ratio of acid/metallic sites.

Amino Acid-Assisted Construction of Single-Crystalline Hierarchical Nanozeolites via Oriented-Aggregation and Intraparticle Ripening.

Hierarchical nanozeolites are highly desired for heavy oil conversion because of their fast mass transfer, good site accessibility, and short diffusion length compared with their conventional counterparts. Here, we provide a facile amino acid-assisted strategy to synthesize hierarchical ZSM-5 (MFI) zeolite nanocrystals by two-step crystallization in a concentrated gel system. Strikingly, each virus-like zeolite nanoparticle with abundant interconnected intracrystalline mesopores is a high-quality single crystal that is defect-free as confirmed by electron diffraction and NMR analysis. By utilizing advanced electron microscopy techniques, we have studied the evolution process of single-crystalline hierarchical ZSM-5 nanocrystals that involves oriented aggregation of protozeolitic nanoparticles formed at low temperature followed by intraparticle ripening at high temperature. The as-prepared hierarchical Ni@ZSM-5 catalysts exhibit superior catalytic performance in hydrodeoxygenation of stearic acid and palm oil.

Role of NiMo Alloy and Ni Species in the Performance of NiMo/Alumina Catalysts for Hydrodeoxygenation of Stearic Acid: A Kinetic Study.

The hydrodeoxygenation (HDO) of vegetable oil and fatty acid is extremely important for the sustainable production of diesel-range hydrocarbons. The present work depicts the role of Ni/Mo (mole) in the performance of alumina-supported NiMo catalysts for the HDO of stearic acid. Both Ni and NiMo alloy coexist in the NiMo catalysts depending on the Ni and Mo content. With increasing Ni/Mo (mole), the NiMo alloy content in the catalyst increases with the simultaneous decrease in the Ni content. The activity of NiMo catalysts thus enhances with increasing Ni/Mo (mole). The reaction follows a decarbonylation route over Ni sites and a HDO route over NiMo alloy species. C17 and C18 alkanes are thus observed as the dominating hydrocarbon product over Ni and NiMo alloy-rich catalysts, respectively. The activity of the NiMo catalyst further enhances with increasing reaction temperature and metal (Ni + Mo) loading. The selectivity to alkanes was, however, not affected by metal loading. A suitable kinetic model was further established based on the reaction mechanism to relate the kinetic data.

Kinetic study of hydrodeoxygenation of stearic acid as model compound for renewable oils

The kinetics during hydrodeoxygenation (HDO) of stearic acid (SA) was investigated to explore the fundamental chemistry and the reaction scheme involved for the reaction with a sulfide NiMo/Al2O3 catalyst. Intermediates like octadecanal (C18O) and octadecanol (C18OH) were used to resolve the reaction scheme and explain the selectivity for the three major reaction routes (decarboxylation, decarbonylation and direct-HDO). Several reaction parameters, like temperature, pressure, feed concentration and batch-reactor stirring rate, were explored for their effect on changes in rate of conversion and selectivity. A weaker dependence on pressure (40–70 bar) and strong dependence on temperature (275–325 °C) was found for the product distribution during HDO of SA. A model based on Langmuir–Hinshelwood type kinetics was developed to correlate the experimental data. The model well predicted trends in variation of selectivities with the reaction conditions, in part by including intermediates like octadecanol and octadecanal and it predicted phenomenon like inhibiting effects of the fatty acid. The proposed kinetic model is expected to be applicable to liquid phase HDO of different renewable feeds containing long chain fatty acids, methyl esters and triglycerides etc.

A cleaner route for hydrodeoxygenation of oleic acid in hexane containing pressurized CO2 over a MCF supported Fe-Pd-Ni trimetallic catalyst

Selective production of octadecane through the hydrodeoxygenation of oleic acid in hexane containing pressurized CO2, a green reaction media, using a mesocellular foam (MCF) supported Fe-Pd-Ni/MCF catalyst was demonstrated in this study. In addition to hexane containing pressurized CO2 playing a key role in directing the hydrotreatment of oleic acid towards hydrodeoxygenation over decarboxylation/decarbonylation, the use of MCF as the support helped achieve higher selectivity for octadecane, the major hydrodeoxygenation product while at the same time completely negating heptadecane, the decarboxylation/decarbonylation product. Negligible diffusion resistance aided by the 3-dimensional cage like structure and large pore opening of MCF, plus a better dispersion of the catalyst were identified as major reasons for enhancement of octadecane yield. An octadecane yield of 93% at 4 h was achieved through an optimization of temperature to 278 °C and a H2 pressure to 40 bars, while the CO2 pressure was kept constant at 20 bars. The activation energy for the hydrodeoxygenation of stearic acid to octadecane was observed to be a 43.6% reduction over the existing literature. An increased spillover of H2 onto the surface of Fe nanoparticles, triggered by an increased sticking capability of H2 on Pd-Ni alloy patches formed on the top Fe nanoparticles, was proposed as the major reason for this acceleration. The proposed catalyst could not only avoid production of undesired decarbonized product heptadecane but also reduce energy requirement to achieve higher yield over reported data due to the lowering of temperature and time, indicating its superiority.

Rate enhancement by Cu in NixCu1−x/ZrO2 bimetallic catalysts for hydrodeoxygenation of stearic acid

The combination of Cu and Ni in bimetallic catalysts on ZrO2, leads to a more efficient HDO of stearic acid.

Influence of synthesis method on molybdenum carbide crystal structure and catalytic performance in stearic acid hydrodeoxygenation

The role of the synthesis method of molybdenum carbide nanoparticle catalysts supported on carbon nanofibers on crystal structure and on catalytic performance in hydrodeoxygenation of stearic acid was investigated. We obtained the cubic phase of molybdenum carbide (α-MoC1-x) by impregnating carbon nanofibers with a solution of (NH4)2MoO4, then exposing them to 20% CH4/H2 at 650 °C for 2 h. When increasing the Mo loading from 7.5 wt% to 20 wt% or using the carbothermal reduction method, i.e. using carbon from the support to reduce the (NH4)2MoO4 precursor at 800 °C for 6 h, the hexagonal phase (β-Mo2C) resulted.Experiments with stearic acid hydrodeoxygenation showed that both phases (7.5 wt% Mo) displayed similar intrinsic activities. However, α-MoC1-x/CNF reached 80% stearic acid conversion after 240 min while the β-Mo2C/CNF catalyst attained the same conversion after 360 min. CO chemisorption results showed that α-MoC1-x/CNF and β-Mo2C/CNF have a similar number of potential active sites (66 and 56 μmol g−1, respectively). We attribute the difference in catalytic performance between α-MoC1-x/CNF and β-Mo2C/CNF to differences in the catalyst’s crystal structure, more specifically, the associated site density. The face-centered cubic α-MoC1-x/CNF has a lower site density (0.1096 Mo atoms Å−²) than the hexagonal close-packed β-Mo2C/CNF (0.1402 Mo atoms Å−²), making the Mo atoms at the surface of the α-MoC1-x phase more accessible for large reactant molecules such as stearic acid thus allowing its convertion in shorter times.

Construction of Bifunctional Co/H-ZSM-5 Catalysts for the Hydrodeoxygenation of Stearic Acid to Diesel-Range Alkanes.

Bifunctional Co/H-ZSM-5 zeolites were prepared by a surface organometallic chemistry grafting route, namely, by the stoichiometric reaction between cobaltocene and the Brønsted acid sites in zeolites. The catalyst was applied to a model reaction of the catalytic hydrodeoxygenation of stearic acid (SA). The cobalt species existed in the form of isolated Co2+ ions at the exchange positions after grafting, transformed to CoO species on the surface of the zeolite, stabilized inside the zeolite channels upon calcination in air, and finally reduced by hydrogen to homogeneous clusters of metallic cobalt species approximately 1.5 nm in size. During this process, the Brønsted acid sites of the H-ZSM-5 zeolites were preserved with a slightly reduced acid strength. The as-prepared bifunctional catalyst exhibited an approximately 16 times higher activity for the hydrodeoxygenation of SA (2.11 gSA gcat-1 h-1 ) than the reference catalyst (0.13 gSA gcat-1 h-1 ) prepared by solid-state ion exchange and a high C18 /C17 ratio of approximately 24. The remarkable hydrodeoxygenation performance of the bifunctional Co/H-ZSM-5 was owed to the effective synergy between the uniformed metallic cobalt clusters and the Brønsted acid sites in H-ZSM-5. The simplified reaction network and kinetics of the SA hydrodeoxygenation catalyzed by the as-prepared bifunctional Co/H-ZSM-5 zeolites were also investigated.

Ni catalyst synthesized by hydrothermal deposition on the polymeric matrix in the supercritical deoxygenation of fatty acids

In the current work, the use of Ni-containing catalyst on the base of hypercrosslinked polystyrene in the stearic acid (SA) hydrodeoxygenation (HDO) in the medium of supercritical n-hexane is presented. The catalyst was synthesized by the hydrothermal deposition of Ni-containing particles into the pores of the polymeric matrix in the medium of superheated water. It was found that the catalyst is characterized by the high surface area and the uniform deposition of the active phase on the catalyst surface. Ni in the catalyst is represented by NiOOH. The mean particle diameter of the active phase was found to be 5.5 nm. The catalyst showed high efficiency in the SA HDO in the medium of supercritical n-hexane reaching the C16–C17 yield up to 90 at 100% substrate conversion. It was shown that the catalyst maintained its activity in minimum five consecutive runs without sufficient loose selectivity.

Deoxygenation of stearic acid with a novel Ni(CO)‐MoS2/Fe3S4 catalyst

AbstractMagnetically recyclable Ni(Co)‐promoted MoS2 catalysts with greigite (G) core were synthesized and their activity and selectivity in hydrodeoxygenation of stearic acid were investigated. The activity of the catalysts tested at 320 °C and H2 initial pressure of 3.5 MPa could be ranked as NiMo/G > CoMo/G > Mo/G. Two main products were detected, C18 (through HDO pathway) and C17 hydrocarbons (through DCO pathway). HDO was the dominant pathway for all of the catalysts. As for the C18/C17 ratio, the catalysts were found to be in the order: Mo/G > CoMo/G ≈ NiMo/G. The Paraffin/Olefin ratio was over 1 for all of the catalysts with NiMo/G showing the highest ratio. Stearic acid was found to have an inhibiting effect on the adsorption of intermediates over the active sites. Moreover, the concentrations of intermediates decreased at high conversions of stearic acid. The formation of the intermediate aldehyde is through C–O hydrogenolysis of the fatty acid following the protonation, dehydrogenation, and hydride addition steps. The same steps were suggested to be involved in the transformation of the aldehyde to the alcohol. Formation of Cn‐1 hydrocarbons was found to be via decarbonylation route. The enhancement of the DCO pathway over the promoted catalysts was related to the electron transfer from the promoting atom to an adjacent sulphur atom and reduction in sulphur‐metal bond strength.

Hydrodeoxygenation of stearic acid and tall oil fatty acids over Ni-alumina catalysts: Influence of reaction parameters and kinetic modelling

Kinetics in the hydrodeoxygenation of stearic acid was investigated over Ni-γ-Al2O3 catalyst. The main variables were catalyst prereduction mode, reaction atmosphere and hydrogen pressure in the total pressure range of 7–30bar. The results revealed that high conversion, 99% in 360min and high selectivity to heptadecane, 97% were achieved at 300°C under 30bar total pressure. The yield of an intermediate hydrogenation product, stearyl alcohol increased with increasing hydrogen pressure as expected. Higher reaction rates and conversion levels were also achieved with the prereduced catalyst and carrying out the reaction in the presence of hydrogen. As a comparison to stearic acid, hydrodeoxygenation of tall oil fatty acids, an industrial feedstock was successfully demonstrated with Ni-γ-Al2O3 under the same conditions. A kinetic model including the pressure effect was derived and applied for data with Ni-γ-Al2O3 as well as for Pd/C, Ni-H-Y-80 and Ni/SiO2 catalysts. The model described well the kinetic data.

Effective Hydrodeoxygenation of Stearic Acid and Cyperus Esculentus Oil into Liquid Alkanes over Nitrogen‐Modified Carbon Nanotube‐Supported Ruthenium Catalysts

AbstractNitrogen‐modified carbon nanotube‐supported ruthenium catalyst was demonstrated to be effective in the conversion of crude cyperus esculentus oil into linear liquid alkanes. The model compound stearic acid was nearly quantitatively converted into liquid alkanes, and the yields of n‐heptadecane and n‐octadecane were 89.5 % and 8.5 %, respectively. The mass yield of liquid alkanes from crude cyperus esculentus oil was 76.6 %, which was very close to the theoretical yield. The catalyst could be reused at least six times without loss of catalytic activity during the conversion of oil. We found that the nitrogen modification of the carbon nanotube support was beneficial to form more Ru0 species, which exhibited excellent catalytic activity and stability towards the hydrodeoxygenation of stearic acid and plant oil.