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The hydrodeoxygenation (HDO) of guaiacol, a model compound of pyrolysis oil, was catalyzed by Al-MCM-41 supported Co and Ni catalysts in a fixed-bed continuous reactor at ambient pressure. The effects of contact time (W/F) and reaction temperature on HDO of guaiacol over the Co and Ni catalyst were studied. Cobalt showed higher activity than nickel...
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Nickel-cobalt bimetallic catalysts supported on high surface area graphite with different Ni:Co ratios (3:1, 2:1 and 1:1) and the monometallic Ni and Co were prepared by wetness impregnation method. The catalysts were tested in hydrodeoxygenation (HDO) of guaiacol in the liquid phase at 50 bar of H2 and 300 °C. The materials were characterized by N...
Citations
... The Ni catalysts possess a high hydrogen activation activity, which favors the promotion of C-C bond breaking and causes methanation and coke formation. On the other hand, Co-based catalysts display a higher activity in HDO reactions via C-O bond cleavage [31,32]. ...
Bio-oil upgrading to produce biofuels and chemicals has become an attractive topic over the past decade. However, the design of cost- and performance-effective catalysts for commercial-scale production remains a challenge. Herein, commercial titania (TiO2) was used as the support of cobalt (Co)-based catalysts (Co/TiO2) due to its low cost, high availability, and practicability for commercialization in the future. The Co/TiO2 catalysts were made with two different forms of TiO2 (anatase [TiO2–A] and rutile [TiO2–R]) and comparatively evaluated in the hydrodeoxygenation (HDO) of 4-propylguaicol (4PG), a lignin-derived model compound. Both Co/TiO2 catalysts promoted the HDO of 4PG following a similar pathway, but the Co/TiO2–R catalyst exhibited a higher activity in the early stages of the reaction due to the formation of abundant Ti3+ species, as detected by X-ray photoelectron spectroscopy (XPS) and hydrogen–temperature programed reduction (H2–TPR) analyses. On the other hand, the Co/TiO2–A catalyst possessed a higher acidity that enhanced propylcyclohexane production at prolonged reaction times. In terms of reusability, the Co/TiO2–A catalyst showed a higher stability (less Co leaching) and reusability compared to Co/TiO2–R, as confirmed by transmission electron microscopy (TEM) and inductively coupled plasma optical emission spectroscopy (ICP-OES) analyses. The HDO of the real bio-oil derived from pyrolysis of Leucaena leucocephala revealed that the Co/TiO2–A catalyst could convert high oxygenated aromatics (methoxyphenols, dimethoxyphenols, and benzenediols) to phenols and enhanced the phenols content, hinting at its potential to produce green chemicals from bio-feedstock.
... The effectiveness of coke removal increases with increased duration and temperature of combustion, depending on the resistance of coke deposits to removal [250]. When regeneration by combustion is carried out, careful analysis of the coke combustion parameters is necessary, as an excessively high temperature used for coke combustion can cause catalyst sintering [251]. Thermal treatments are often used to regenerate catalysts; they can be carried out in the presence of air, inert gas, or other gases such as H 2 and CO. ...
The environmental impact of traditional fuels and related greenhouse gas emissions (GHGE) has promoted policies driven towards renewable fuels. This review deals with green diesel, a biofuel obtained by catalytic deoxygenation of edible and non-edible biomasses. Green diesel, biodiesel, and petrodiesel are compared, with green diesel being the best option in terms of physical–chemical properties and reduction in GHGE. The deoxygenation process and the related types of catalysts, feedstocks, and operating conditions are presented. Reactor configurations are also discussed, summarizing the experimental studies. Several process simulations and environmental economic analyses—up to larger scales—are gathered from the literature that analyze the potential of green diesel as a substitute for petrodiesel. In addition, current industrial processes for green diesel production are introduced. Future research and development efforts should concern catalysts and the use of waste biomasses as feedstock, as well as the arrangement of national and international policies.
... These alkyl transfer reactions are catalyzed by the acid sites of the support material and helped to preserve the carbon in the liquid products. As expected in the presence of support alone, 1-2 dimethoxybenzene was mainly observed in the liquid phase [68][69][70]. ...
Tungstated zirconia supported Ni catalysts with different Ni contents (3 to 20 of % w/w) were synthesized at mild conditions in a stirred pressure reactor. We reported multi-objective optimization (MOO) of tungstated zirconia preparation in terms of Brønsted acid site density and surface area for the first time in the open literature. Optimization of nickel content was also performed in terms of HDO activity and selectivity. Obtained MOO results showed that optimum nickel content was 15% in terms of selectivity and activity. Predicted response results were in good agreement with the experimental response results. The catalytic performance of the catalyst samples was tested on the HDO reaction of guaiacol. Additionally, an HDO mechanism for Ni-doped WOxZrO2 catalyzed guaiacol conversion was proposed. High activity and selectivity rates were achieved during the experiments and cyclohexane was obtained as a main product in the presence of more than 10% of Ni-doped tungstated zirconia catalyst.
... Transition metals (TMs) such as Ni and Co have emerged as alternative candidates due to their abundance and performance in hydrogenation reactions (Song et al., 2015;Fang et al., 2017). Indeed, several experiments have considered TMs as HDO catalysts, e.g., Fe (Olcese et al., 2012;Olcese et al., 2013), Co (Tran et al., 2016a;Tran et al., 2016b;Han et al., 2019), Ni (Zhao et al., 2011;Tran et al., 2016a), Cu (Deutsch and Shanks, 2012), Pd (Nimmanwudipong et al., 2011;Silva et al., 2021) and Pt (Nimmanwudipong et al., 2011;Silva et al., 2021), showing different selectivity as a function of the support, reaction temperature, and H 2 partial pressure. These TMs have also been highlighted previously due to their oxygen and hydrogen affinity (Morteo-Flores et al., 2020). ...
... The guaiacol HDO mechanism takes place through three different main pathways to form anisole, phenol and catechol compounds: dehydroxylation (C aryl −OH), demethylation (C alkyl -O) and demethoxylation (C aryl −OCH 3 ) Infantes-Molina et al., 2015;Teles et al., 2018;Phan et al., 2020). Different HDO experiments on TMs have also highlighted the presence of methane, water, and methanol in the products mixture (Tran et al., 2016b). Sun et al. studied the HDO of guaiacol on TM catalysts supported on carbon, e.g., Cu, Fe, Pd, Pt, and Ru. ...
Understanding the mechanisms of guaiacol’s catalytic hydrodeoxygenation (HDO) is essential to remove the oxygen excess in bio-oils. The present work systematically examines guaiacol’s HDO mechanisms to form benzene on six transition metal (TM) catalysts using density functional theory calculations. The results suggested a preferable Caryl−O bond scission on Ni (111) and Co (0001), whereas on Fe (110), the Caryl–OH bond scission is the most likely pathway. The C−O scission on Pd (111) and Pt (111) is not energetically feasible due to their high activation barriers and endothermic behaviour. Fe (110) also demonstrated its high oxophilic character by challenging the desorption of oxygenated products. A detailed analysis concludes that Co (0001) and Ni (111) are the most favourable in breaking phenolic compounds’ C−O type bonds. Brønsted-Evans-Polanyi (BEP) and transition state scaling (TSS) models were implemented on the catalytic results to derive trends and accelerate the catalyst design and innovation. TSS demonstrated a reliable trend in defining dissociation and association reaction energies. The phenyl ring-oxo-group and the metal-molecule distances complement the catalysts’ oxophilicity as selectivity descriptors in the HDO process.
... 24 Non-noble metals, such as Ni, Cu, and Co-based catalysts, 25−35 also show good performance, are advantageous due to their lower costs, and appear to be highly active for the obtention of cyclohexanol, especially nickel and Co-based catalysts, where Co catalysts were generally more active than Ni 29,33 but more selective toward phenol. 33 However, besides their high activity, Ni catalysts suffer from deactivation 36−39 which was mainly due to coke deposition or metal sintering. 40,41 Typically, to prevent the metal sintering, two strategies can be explored: the use of bimetallic systems 42 or the modification of the support. ...
... It can be observed that Ni is less active than Co when supported over both nitrogen-doped and undoped GOr in agreement with previous results over other carbon supports 53 and over Al-MCM-41 or zirconium phosphate (ZrP) or zeolites. 29,33,73 However, better hydrogenation activity of Ni compared to Co has also been reported for SBA-15 based catalysts in the gasphase HDO of anisole 74 and over CeO 2 for in situ hydrogenation using alcohols as hydrogen donors. 75 Moreover, the doped samples display better activity than their undoped counterparts. ...
... 21 DFT calculations have also proved a synergistic effect between Pt and MOx species in adsorbing/activating C−O bonds, making metal−metal oxide catalysts interesting and promising for HDO. 22 The use of new supports such as nanotubes, 23 orderedmesoporous silica, 24,25 and different types of carbon, 26 has attracted the attention of researchers, because of their properties, such as high surface area, porosity, acidity, or basicity, etc. Among such supports, Sibunit, which is a type of mesoporous, microcrystalline carbon, is considered as an attractive material, because of its high mechanical strength, 27 reasonably large surface area, high purity, and chemical stability, 28 combining the properties of graphite and activated carbon. ...
A series of monometallic platinum and bimetallic platinum–rhenium catalysts supported on mesoporous carbon Sibunit, which is a type of mesoporous, microcrystalline carbon, were investigated for hydrodeoxygenation (HDO) of isoeugenol (IE) at 200–300 °C and 30 bar of H2, using dodecane as a solvent. Catalytic activity was tested in a batch reactor to screen the catalysts and, for comparison, also in the continuous mode. For batch experiments, complete conversion, and a high yield of the desired product, propylcyclohexane (PCH), were obtained for all bimetallic PtRe/Sibunit in 240 min, with the highest yield of PCH when Pt:Re ratio was 1:1 or 1:3. The results for Pt–Re (1:1) were reproducible, in terms of catalytic activity and reusability of catalysts, which showed no deactivation. Monometallic Pt catalysts displayed low activity. Continuous experiments were performed with PtRe(1:1)/Sibunit at 30 bar H2, 0.5 mL/min of the liquid flow, and temperatures between 75 °C and 200 °C. The distribution of products showed deoxygenation at higher temperatures, while at lower temperatures, mainly oxygenated products were formed. XPS results confirmed the presence of ReOx species, where an increase in the platinum loading resulted in a decrease in the fraction of ReOx species and subsequently lower PCH yield.
... Further increase in temperature to 450 °C led to hydrogenolysis of the hydroxyl group in cresol resulting in the formation of toluene. Apart from these major pathways, demethylation of methoxy group in guaiacol to produce catechol is reported as a possible route in several other studies using different catalysts [18,19]. However, due to the absence of catechol in the product spectrum, this pathway is not considered in this study. ...
This study is focused on understanding the hydrodeoxygenation (HDO) kinetics of pyrolysates from lignin such as phenol, guaiacol and syringol over H-ZSM-5 catalyst. The major products from syringol were guaiacol, phenol, anisole, cresol, benzene, and toluene. A reaction network was proposed to capture the transformations of syringol in which the transformations of guaiacol and phenol were included. A kinetic model comprising nine reactions of seven species was developed. The simulated yields of a majority of the HDO products matched well with experiments in the temperature range of 350-500 °C, substantiating that the obtained rate parameters reasonably represent the HDO kinetics.
... All catalysts sample presented spherical small crystallites alternating between welldefined structures to greater particle nonuniform clusters. This morphology characteristics is typical for Al-MCM-41 and the more aluminum is inserted into the MCM-41 matrix structure itself, the greater the tendency to observe a more dispersed material containing a less defined morphology [52,[62][63][64]. ...
In this work, Al-MCM-41 molecular sieves were synthesized, containing iron and/or cobalt oxides, impregnated by incipient wetness method, characterized and applied as catalysts in the acetylation reaction of glycerol with propionic acid to produce green glyceryl propionate molecules of high commercial value. According to this, X-ray Diffraction (XRD), X-ray Fluorescence (XRF), Fourier Transform Infra Red (FT-IR), adsorption/desorption N2 isotherms, textural analysis, and Scanning Electron Microscope (SEM) analysis were recorded to evaluate the main characteristics of materials. The presence of Lewis and Brønsted acidic sites and catalysts surface area were observed as important key points to function-alize acetylation reaction. Thus, time reaction, temperature, and glycerol / propionic acid ratio varied to improve the most suitable reaction conditions and behaviors. As a result, glycerol conversion was above 96%, followed by 68% of selectivity to glyceryl monopropionate as well as the formation of glyceryl di-and tri-propionate and a small amount of ethylene glycol dipropionate as an undesired product.
... Non-noble metal has attracted the attention of the obtention of cyclohexanol, especially nickel-based catalysts [16][17][18]. Cobalt-based catalysts have been studied less, but have been found to be active for HDO reactions [19][20][21][22]. ...
... Ni/G NiCo 3:1 /G For the monometallic catalysts, Ni catalyst displayed a lower activity than Co catalyst. This behavior has already been reported in other cases, such as Ni/Co supported over Al-MCM-41 or Zirconium phosphate (ZrP) [22,49]. To better observe the effect of the bimetallic systems compared to the monometallic catalysts, we have represented in Figure 6 the theoretically expected trend (dotted line) if there were no interaction or synergy between the two metals, along with the estimated experimental values (symbols). ...
Nickel-cobalt bimetallic catalysts supported on high surface area graphite with different Ni:Co ratios (3:1, 2:1 and 1:1) and the monometallic Ni and Co were prepared by wetness impregnation method. The catalysts were tested in hydrodeoxygenation (HDO) of guaiacol in the liquid phase at 50 bar of H2 and 300 °C. The materials were characterized by N2 adsorption–desorption, XRD, TEM/STEM, H2-TPR, and CO-chemisorption to assess their properties and correlate them with the catalytic results. The activity was higher on the bimetallic catalysts and followed the trend NiCo2:1/G ∼ NiCo3:1/G > NiCo1:1/G > Co/G > Ni/G. Also, selectivity results showed that Ni was more active in the hydrogenation favoring cyclohexanol production from phenol, while this was inhibited on the Co-containing catalysts. Hence, the results showed that synergy was created between Ni and Co and that their interaction, properties, and catalytic performance depend on the metals’ ratio.
... In addition, ZSM-5 was reported to facilitate the formation of aromatics during the pyrolysis of biomass, while zeolites with large internal pore space such as Y and Beta display poor selectivity towards larger aromatic molecules and promote the formation of coke [27]. The mesoporous Al-MCM-41 was employed to study guaiacol HDO at atmospheric hydrogen pressure, however, high reaction temperature was required and high phenol selectivity was detected, indicating a lower deoxygenation activity [28,29]. ...
The influence of catalyst pore size and shape selectivity on the catalytic hydrodeoxygenation (HDO) of biocrude oil has been investigated by comparing the activity of nickel catalysts on the supports of different pore sizes towards model compounds of increasing size. The catalysts (Ni/Beta and Ni/Y) with 3-dimensional structure containing 12 × 12-ring channels show a higher hydrogenation activity for phenanthrene compared to 10 × 10-ring and 12 × 8-ring channel catalysts (Ni/ZSM-5 and Ni/MOR), while only Ni/Y, possessed the largest pore limiting diameter (7.4 Å), displays a good hydrogenation activity for pyrene (6.7 Å), the model compound with the largest critical diameter studied in this work. While all catalysts display a good HDO activity for guaiacol conversion, the 10 × 10-ring channel catalyst (Ni/ZSM-5) exhibit a lower cyclohexane formation rate compared to catalysts containing 12-ring channels when the residence time was reduced, which could be attributed to the small pore diameter (5.0 Å) of ZSM-5 that restricts the diffusion of guaiacol (∼4.9 Å). In addition, the Ni/Beta and Ni/ZSM-5 were also tested in HDO of biocrude oil. Ni/Beta catalyst displays higher conversion and high yield of cycloalkanes compared to Ni/ZSM-5, which confirms that the selection of catalyst support has a significant influence on the product distribution in HDO of biocrude.
