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Effective hydrodeoxygenation of biomass-derived oxygenates into unsaturated hydrocarbons by MoO3 using low H2 pressures
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Effective hydrodeoxygenation of biomass-derived oxygenates is achieved with MoO3 to produce unsaturated hydrocarbons, converting linear ketones and cyclic ethers to olefins, and cyclic ketones and phenolics to aromatics with high yields. The catalyst is selective for C-O bond cleavage and operates using low H2 pressures ([less-than-or-equal]1 atm). We show that deactivation can be minimized by tuning hydrogen partial pressure, that original activity can be recovered by calcination, and that catalytic activity is maintained in the presence of water. Theoretical calculations are used to elucidate reaction pathways and highlight the role oxygen vacancies during the deoxygenation process.
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... Reaction energies in 2nd HDL of 2-Methyloxolane and 3-Methyloxolane are positive and leading to an endothermic reaction in nature, due to the position of the methyl groups on the ring of the Oxolane molecule. The reaction energies of our designed pathway are more than already reported reaction energies for deoxygenation of biofuels to valuable fuels, using MoO 3 as catalyst for this conversion [62]. ...
The persistent global demand of fossil fuels has spurred significant interest in the invention of new renewable energy sources to replace finite, non-renewable fossil fuels. Among these sustainable energy options, biomass stands out as a promising candidate as environment friendly alternative fuel. However, the organic compounds found in biomass contain a high oxygen content, leading to several undesirable characteristics in biofuels, including low energy density, less stability, high viscosity, and corrosion. Consequently, researchers have devised various upgrading techniques, with a particular emphasis on the hydrodeoxygenation (HDO) process, to enhance the quality of biofuel. In this report, we investigated the treatment of Oxolane, 2-Methyloxolane and 3-Methyloxolane via adsorption and catalytic hydrogenolysis (HDL) processes. These processes aim to remove the oxygen heteroatom from these compounds, ultimately achieving the desired purity levels. To elucidate the underlying mechanisms, we employed the B3LYP/6–31G(d) and LanL2DZ/6–31G(d) methods of DFT for reaction without or with catalysts. The hydrogenolysis, in the presence and absence of a catalyst is carried at a temperature and pressure of 523 K and 40 bar, respectively. We meticulously analyzed the variations in geometries, thermodynamic and kinetic properties to gain insights into the whole processes. For each molecule, the sequence involves ring opening of C–O bond, followed by the elimination of a water molecule. The first hydrogenolysis step yields an alcohol as a reaction intermediate, while the second hydrogenolysis step results in the formation of an alkane. Geometric parameters showed the increased reactivity of Oxolane and its derivatives in the presence of tungsten disulphide (WS2) catalyst. Chemical potential indicates the charge transfer occurred in all, and the highest charge transfer is observed in Oxolane in the presence of tungsten disulphide (WS2) catalyst.
... Different type of HDO catalytic materials have been investigated the last years, such as noble metal catalysts (Pd, Pt, Ru, Rh) 15 , zeolites 16 , non-noble metals (Ni, Cu) 17,18 and catalysts based on transition metal oxides, such as Mo and W 11 . Among those, Mo-based catalysts have attracted much attention [19][20][21] . Likozar's group have studied HDO of lignocellulosic biomass by using Mo-based catalysts, as well Pd, Ni either unsupported and/or supported on different supports. ...
In this work, the reaction pathways of one-step glycerol hydrodeoxygenation in gas phase is exploited under flow conditions over molybdena-based catalyst (8.7 wt% Mo/black carbon). Hydrodeoxygenation (HDO) experiments with possible...
Molybdenum oxide-based catalysts are promising catalysts for the gas-phase hydrodeoxygenation (HDO) of lignocellulosic pyrolysis oils with high selectivities to arenes. The gas-phase HDO is conducted at temperatures between 300 °C...
Cobalt molybdate (CoMoO 4 ) was synthesized by a simple and environmentally friendly evaporation method and it exhibited excellent catalytic performance for the selective hydrodeoxygenation of lignocellulosic ketones to their corresponding olefins.
The conversion of compounds representative of lignin and lignin-derived bio-oils (guaiacol, anisole, 4-methylanisole, and cyclohexanone), catalysed by Pt/Al2O3 in the presence of H2 at 573 K is described by a reaction network indicating a high selectivity for platinum-catalysed aromatic carbon–oxygen bond cleavage accompanied by acid-catalysed methyl group transfer reactions.
The studies on hydrogen reduction of MoO3 indicated two main stages, namely, MoO3 to MoO2 and MoO2 to Mo. In both stages, temperature and time of reduction progressively increased on diluting hydrogen from 100 to 10 pct. Detailed kinetic analysis of the MoO2 to Mo stage was conducted by carrying out isothermal reduction between 625 °C and 900 °C by pure hydrogen. The kinetic equation was found to be
$$ g{\left( \alpha \right)} = {\left[ { - \ln {\left( {1 - \alpha } \right)}} \right]}^{{\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 n}}\right.\kern-0em} \!\lower0.7ex\hbox{$n$}}} = {\text{k}}t $$
, with n ranging from 1.49 to 2.13. The rate constant k obeyed the Arrhenius temperature dependence with the associated activation energy of 136 kJ mol−1. The X-ray diffraction (XRD) analysis of the product confirmed the phases predicted by thermal analysis. The scanning electron microscope (SEM) analysis of molybdenum powder revealed the presence of a greater number of pores and cracks in the individual particles produced at lower reduction temperatures and the tendency of acquiring spherical morphology with increasing reduction temperature. Based on the studies conducted, the optimum conditions for MoO3 to Mo reduction were predicted.
Catalytic hydrotreatment or hydrodeoxygenation (HDO) has been researched extensively with the crude bio-oil and its model compounds over conventional sulfided Ni(Mo), Co(Mo) catalysts and supported noble metal catalysts. These types of catalysts showed themselves unsuitable for the target HDO process, which resulted in an urgent need to search for a new catalytic system meeting such requirements as low cost, stability against coke formation and leaching of active components due to adverse effect of the acidic medium (bio-oil). In the present work a series of Ni-based catalysts with different stabilizing components has been tested in the hydrodeoxygenation (HDO) of guaiacol (2-methoxyphenol), bio-oil model compound. The process has been carried out in an autoclave at 320 °C and 17 MPa H2. The main products were cyclohexane, 1-methylcyclohexane-1,2-diol, and cyclohexanone. The reaction scheme of guaiacol conversion explaining the formation of main products has been suggested. The catalyst activity was found to rise with an increase in the active component loading and depend on the catalyst preparation method. The most active catalysts in HDO of guaiacol were Ni-based catalysts prepared by a sol–gel method and stabilized with SiO2 and ZrO2. According to TPR, XRD, XPS, and HRTEM, the high activity of these catalysts correlates with the high nickel loading and the high specific area of active component provided by the formation of nickel oxide–silicate species. The effect of temperature on the product distribution and catalyst activity in the target process (HDO) has been investigated as well. The catalysts were shown to be very promising systems for the production of hydrocarbon fuels by the catalytic upgrading of bio-oil.
Water formed during hydrotreating of oxygen-containing feeds has been found to affect the performance of sulphided catalysts in different ways. The effect of water on the activity of sulphided NiMo/γ-Al2O3 and CoMo/γ-Al2O3 catalysts in hydrodeoxygenation (HDO) of aliphatic esters was investigated in a tubular reactor by varying the amount of water in the feed. In additional experiments, H2S was added to the feed, alone and simultaneously with water.Under the same conditions, the NiMo catalyst exhibited a higher activity than the CoMo catalyst. The ester conversions decreased with increase in the amount of added water. When H2S and water were added simultaneously, the conversion increased to the same level as without water addition on the NiMo catalyst and reached a higher value on the CoMo catalyst. The conversions were highest, however, when only H2S was added. Unfortunately, the conversions decreased with time under all conditions. On both catalysts, the total yield of the C7 and C6 hydrocarbons decreased with the amount of added water, while the concentrations of the oxygen-containing intermediates increased. The presence of H2S improved the total hydrocarbon yield and shifted the main products towards the C6 hydrocarbons. Thus, the addition of H2S effectively compensated the inhibition by water.
The selective oxidation of propene on the vanadyl and bridging oxygen sites of the fully oxidized (0 0 1) V2O5 surface and of an epitaxial vanadia monolayer supported on (0 0 1) TiO2 anatase is analyzed using periodic density functional theory (DFT). The formation of several oxygenated products, that is, allyl alcohol, propene oxide, acrolein, formaldehyde and acetaldehyde, is investigated. Selective oxidation proceeds via a Mars–van Krevelen redox mechanism and its elementary steps on the vanadia surface are identified. Propene activation occurs preferentially on the vanadyl oxygen sites, with allyl CH and CC bond activation being equally favorable. Supporting a vanadia monolayer on titania strongly enhances both bond activations as compared to unsupported V2O5, yielding a lower activation energy. No dominant pathway is found on V2O5, with allyl alcohol, propene oxide, and acrolein formation being almost equally favorable, while acrolein formation is expected on V2O5/TiO2. However, propene oxidation to acrolein is overall less preferable on V2O5/TiO2 than V2O5, due to the reduced activity of the supported catalyst in oxygenation reactions. The latter is linked to the creation of V3+ sites during propene oxidation over V2O5/TiO2. On the other hand, the electrons injected in the empty V 3d states during propene oxidation over V2O5 lead to the creation of V4+ sites.
The conversion of furfural (FAL) and 2-methylpentanal (MPAL) under hydrogen has been studied over silica-supported monometallic Pd and bimetallic Pd–Cu catalysts. At low space times, the conversion of MPAL yields primarily pentane (decarbonylation), but at higher space times, di-methylpentyl ether (etherification) becomes the main product. Upon addition of Cu, both the overall activity and the decarbonylation selectivity decrease while the selectivity to hydrogenation and etherification increases. In contrast to MPAL, the conversion of FAL shows no etherification products at any space time in the temperature range 210–250 °C but only produces furan via decarbonylation. It is proposed that the presence of the aromatic ring in the furfural molecule has a marked effect in inhibiting the formation of the alkoxide surface intermediate, which is required in the etherification reaction. Density Functional Theory (DFT) calculations of furfural and 2-methyl pentanal have been conducted to gain a better understanding of the differences in the molecule–surface interactions between the aldehydes and the Pd and Pd–Cu surfaces. The reaction mechanisms and the resulting selectivity towards the possible reaction paths (hydrogenation/etherification/decarbonylation) are discussed in terms of the relative stability of the η2-(C,O) and acyl surface species occurring on the different metal surfaces.
1H NMR solid state techniques have been used to study bonding properties, location, and mobility of hydrogen in various phases of the hydrogen bronze HxMoO3. Temperature‐dependent spectra characteristic of different degrees of intercalation have been observed, and furthermore, from measurements of the relaxation rate, dynamic properties have been derived. There is strong evidence of intralayer hydrogen positions on a quasi‐one‐dimensional zig–zag line connecting the vertex‐sharing oxygen atoms of the MoO6 octahedra and these are first occupied if the degree of intercalation x is low. For x>0.85 the hydrogen in excess starts to fill up interlayer positions coordinated with terminal oxygen atoms at the van der Waals gap. Both isolated and paired protons have been detected in the interlayers, whereas clusters or pairs appear along the zig–zag lines. Hydrogen separations within the clusters, bonding with oxygen and charge transfer to the conduction band of the host lattice, are discussed. Hydrogen diffusion changes from being predominantly one‐dimensional to three‐dimensional in character as x increases. The activation energies of the motion are of the order of magnitude of 15 to 30 kJ/mol.
Detailed interpretation of EPR signals appearing in commercial MoO3 upon reduction invacuo at different temperatures is presented. New O- species in the MoO3 bulk and Mo5+ ions without a molybdenyl bond have been found under such conditions, their intensities depending on temperature and time of reduction. It is argued that formation and stabilization of these unusual species is related to traces of nitrogen impurities. A model of redox processes occurring in MoO3 upon gradual loss of the lattice oxygen and during reconstruction of the MoO3 lattice upon reoxidation of reduced MoO3, involving O- species, as an intermediate stage, is suggested.