Hydrodeoxygenation Of M-cresol Research Articles

Optimization of catalyst activity and stability in the m-cresol hydrodeoxygenation through Ni particle size control

By taking advantage of different nanoparticle size control methodologies, the precise role of Ni particle size (from 1 nm to 9 nm) was evaluated in the HDO of m-cresol in vapor phase at 573 K under atmospheric pressure. The m-cresol HDO reaction pathways were found to be Ni-particle size dependent. The direct deoxygenation (DDO) rate increased by 10 times when decreasing Ni particle size from 9 nm to 1 nm, while the hydrogenation (HYD) and hydrogenolysis (HYG) rates moderately increased. By applying a geometric model, reaction rates were correlated to the different type of sites. Edges and corner sites (smaller particles) favor aromatics production (DDO route), while face sites (larger particles) favor both HYD and HYG routes. Catalysts partially deactivated due to coke formation, with only slight sintering observed for 1 nm Ni particles. Such findings may serve in the further preparation of active and selective catalysts for bio-oils upgrading into fuel.

Origin of strong metal-support interactions between Pt and anatase TiO2 facets for hydrodeoxygenation of m-cresol on Pt/TiO2 catalysts

Metal/reducible metal oxide catalysts are widely used in hydrodeoxygenation (HDO) reactions for upgrading bio-oil to produce chemicals and fuel components. Under such strong reducing condition, the strong metal-support interaction (SMSI) should take place, however, few work has been devoted to understand the effect of facet of metal oxide on the SMSI and its consequence on HDO performance. Herein, Pt supported on anatase TiO2 with varying dominative exposed facets of (101), (100) and (001) were prepared and tested in HDO of m-cresol at 350 °C and atmosphere H2 pressure. The degree of SMSI of Pt/TiO2 is strongly dependent on the facet of TiO2 when reduced at 350 °C, and the degree of encapsulation decreases following the order of Pt/TiO2-100 > Pt/TiO2-001 > Pt/TiO2-101. The encapsulation correlates well with the reduction degree of TiO2 and the location of oxygen vacancy, which are resulted from varied oxygen vacancy formation and anisotropic diffusion rates in different facets. The intermediate SMSI is achieved on TiO2-001, which creates the maximal density of Pt-Ov-Ti3+ sites at the interfacial perimeter of TiOx/Pt for deoxygenation of m-cresol, resulting in the highest reaction rate and turnover frequency (TOF) while the lowest activation energy (Ea). In contrast, the maximum SMSI on TiO2-100 leads to the lowest deoxygenation rate while the highest Ea. This work provides insight into facet dependent SMSI of Pt/TiO2 and indicates the HDO activity can be finely tailored by tuning the facet of TiO2.

Comparative study of hydrodeoxygenation performance over Ni and Ni2P catalysts for upgrading of lignin-derived phenolic compound

To deeply understand the different hydrodeoxygenation (HDO) behavior of the monometallic Ni and Ni2P catalysts in HDO processes, the Ni/SiO2 and Ni2P/SiO2 catalysts were prepared, respectively. The as-prepared catalysts were characterized by X-ray diffraction (XRD), N2 adsorption–desorption, X-ray photoelectron spectra (XPS), H2 temperature-programmed reduction (H2-TPR), transmission electron microscope (TEM), NH3 temperature-programmed desorption (NH3-TPD), and CO uptakes. Taking the lignin-derived phenolic compound as raw material, the HDO performance and reaction route of the monometallic Ni and Ni2P catalysts were compared. The results showed that the phosphorization contributed to highly dispersion of active sites, formation of smaller active sites and significantly enhanced acid sites, showing Ni2P/SiO2 catalyst is a bifunctional metal–acid catalyst. For both of the Ni/SiO2 and Ni2P/SiO2 catalysts, the HDO of m-cresol mainly proceeded by the hydrogenation (HYD) step. However, the acid sites on Ni2P/SiO2 catalyst can significantly promote the conversion of oxygenated 3-methylcyclohexanol (MCHnol) to deoxygenated methylcyclohexane (MCH) owing to its strong hydrogenolysis of C–OH bond originated from the bifunctional metal–acid sites. In addition, the unique electron structure of Ni2P phase involved in two different types of sites (tetrahedral Ni(I) and square pyramidal Ni(II)) and the highly dispersed smaller Ni2P particles also contributed to the outstanding HDO performance. Density functional calculation (DFT) calculations clarified that the Ni2P active phase possessed prior ability to cleavage of C–OH bond in comparison with the metallic Ni species. As a result, Ni2P/SiO2 catalyst showed a significantly higher selectivity to MCH (96.3 %) than that of Ni/SiO2 (14.1 %) catalyst at the conditions of 250 ℃ for 240 min.

Hydrodeoxygenation of m-cresol over Pd/Al-SBA-15 catalysts: Effect of Al content on the deoxygenation reaction pathways

The effect of aluminium content (x = 5, 20 and 40 wt %) in SBA-15 type silica supports used to obtain Pd/xAl-SBA-15 catalysts was evaluated in the HDO reaction of m-cresol at 300 °C, under atmospheric and high (30 bar) pressure. Aluminium incorporation was performed using the two-step pH-adjustment method, affording the deposition of Al phases over silica previously precipitated. Pd was thereafter deposed using incipient wetness impregnation. Physico-chemical properties of the catalysts were investigated by XRD, N2 physisorption, H2 chemisorption, DRIFTS of adsorbed pyridine, STEM-EDX mapping coupled to HAADF imaging. The acidity (Brønsted and Lewis sites) generated by the incorporation of aluminium at low content (i.e. 5 wt %) onto the SBA-15 structure resulted in the improvement of HDO of m-cresol, with an increase in selectivity toward the deoxygenated products, toluene under atmospheric pressure (38 % for the Pd/SBA vs. 77 % for the Pd/Al5-SBA) and methylcyclohexane under high pressure (14 % for the Pd/SBA vs. 30 % for Pd/Al5-SBA). The selectivity into methylcyclohexanone was also affected by the total pressure: 5 % under atmospheric pressure vs 64 % under 30 bar over Pd/Al5-SBA). However, under atmospheric pressure, at higher Al contents, side reactions catalyzed by acid sites were promoted, such as isomerization and disproportionation reactions, which were not observed under high pressure. Besides that, the increase of quantity of Al leaded to the decrease of the surface accessibility and hence drop on the reactions rate over both pressure conditions. This work demonstrated the efficiency of Pd catalyst in HDO reaction which can be obtained by a precise adjustment of the quantity of Al in the SBA catalytic support.

Selective upgrading of biomass-derived benzylic ketones by (formic acid)–Pd/HPC–NH2 system with high efficiency under ambient conditions

Selective upgrading of biomass-derived benzylic ketones by (formic acid)–Pd/HPC–NH2 system with high efficiency under ambient conditions

The effects of SMSI on m-Cresol hydrodeoxygenation over Pt/Nb2O5 and Pt/TiO2

The hydrodeoxygenation (HDO) of m-cresol was studied on Pt/Nb2O5/MgAl2O4 and Pt/TiO2/MgAl2O4 catalysts to understand the effects of Strong Metal Support Interactions (SMSI). The Nb2O5 and TiO2 supports were prepared as 0.7-nm films on MgAl2O4 by Atomic Layer Deposition (ALD) to ensure that the structures of the catalyst were the same. When reduced at 773 K to place Pt in the encapsulated state, Pt/Nb2O5/MgAl2O4 was much less active than Pt/MgAl2O4 at 573 K but much more active at 623 K. While Pt/MgAl2O4 deactivated rapidly due to coking, Pt/Nb2O5/MgAl2O4 showed significantly better coke tolerance and was almost 100% selective towards toluene production. Pt/Nb2O5/MgAl2O4 reduced at lower temperatures exhibited intermediate catalytic properties. The effect of reduction temperature on Pt/TiO2/MgAl2O4 was much less and this catalyst was more similar to Pt/MgAl2O4 than its Nb2O5 counterpart. The implications of these results for understanding the nature of oxide promoters on HDO of m-cresol are discussed.

Direct Hydrodeoxygenation of m-Cresol to Toluene over Bifunctional NbOx–Pt

This study compared the hydrodeoxygenation (HDO) of m-cresol over Pt and NbOx-modified Pt catalysts. Reactivity measurements demonstrated that Pt supported on carbon (Pt/C) has moderate selectivity for the production of toluene during the HDO of m-cresol, with a range of ring saturation products also being produced. The modification of Pt with niobium (NbOx–Pt/C), however, was found to enhance the selectivity to toluene to 95%. Temperature-programmed desorption, X-ray photoelectron spectroscopy, and high-resolution electron energy loss spectroscopy studies of model Pt(111) single crystal catalysts were used to provide insight into the mechanism by which the niobium enhances the selectivity. These studies showed that interactions at the NbOx–Pt interface help maintain the niobium in a partially reduced state that contains unsaturated Nb cations, which provide adsorption sites on which m-cresol undergoes direct C–O bond hydrogenolysis to produce toluene.

Hydrodeoxygenation of m-Cresol over Ru based catalysts: Influence of catalyst support on m-Cresol conversion and methylcyclohexane selectivity

The hydrodeoxygenation (HDO) of m-Cresol (a representative of lignin bio-oil) has enormous potential for the production of valuable compounds. The products obtained from HDO of m-Cresol (m-Cr) are blendable into conventional fuels and essential for chemical industries such as plastic, fiber, rubber, resin, film, and coating industry. Ruthenium loaded acidic supports (ZSM-5, β-zeolite, y-zeolite, mordenite, COK12, ZrO2, TiO2) were used for the selective hydrodeoxygenation of m-Cresol into methylcyclohexane (MCXane). The effects of acid sites, as well as the pore size of the different supports on the hydrodeoxygenation activity and selectivity towards methylcyclohexane were addressed. The methylcyclohexane yield increased with increasing number of acid sites up to optimum acidity (532 μmol/gm) along with pore size (5.9 Ao). The experiments were carried out at 225–325 °C and 1–40 bar hydrogen pressure in a fixed bed reactor and observed that reaction temperature, and hydrogen pressure promoted the hydrodeoxygenation. The Ru/ZSM-5 is a stable (240 h) catalyst and displayed excellent behavior in both hydrodeoxygenation activity (100%) and methylcyclohexane selectivity (100%) for m-Cresol.

Hydrodeoxygenation of m-Cresol Over Pt-WOx/C Using H2 Generated In Situ by n-Hexane Dehydrogenation

Hydrodeoxygenation (HDO) of m-cresol using H2 produced by dehydrogenation of n-hexane to hexenes is demonstrated at 673 K over a Pt-WOx/C catalyst at 36 bar. The reaction is possible because deactivation of Pt/C during n-hexane dehydrogenation is greatly suppressed at higher pressures. Flow-reactor measurements of pure n-hexane over Pt/C showed rapid deactivation at 1 bar and 773 K but the catalyst was stable for at least 5 h at 36 bar. While the Pt/C catalyst showed poor activity for HDO of m-cresol, the Pt-WOx/C catalyst was able to utilize the H2 to selectively catalyze m-cresol to toluene, simultaneously pushing the conversion of n-hexane above the equilibrium value that would be achieved in the absence of H2 consumption. To explain the increased stability for alkane dehydrogenation at higher pressures, a microkinetic model of propane dehydrogenation, a surrogate of hexane, was analyzed. The model demonstrates that the coverage of vacancies increases with increasing pressure at the expense of species believed to be coke precursors.

Effect of acid-metal balance of bifunctional Pt/Beta catalysts on vapor phase hydrodeoxygenation of m-cresol

Abstract Metal/zeolite bifunctional catalysts have been widely explored for hydrodeoxygenation (HDO) of phenolics. However, the effect of acid-metal balance is not clearly understood because it is difficult to decouple this from other effects. In this work, a series of 1 wt.% Pt/Beta catalysts with different Bronsted acid site (BAS) to surface Pt ratios (BAS/Pt) were prepared by varying only the density of BAS, and tested in HDO of m-cresol at 250 °C and atmospheric pressure. Increasing BAS density increases intra-crystallite diffusion constraints of m-cresol/products due to strong chemisorption on BAS, and therefore slows their transportation through BASs toward the Pt sites inside the micropores of zeolite. As a result, both the reaction rate and turnover frequency of HDO are reduced with increasing BAS/Pt ratio. Increasing BAS/Pt ratio increases the yield of ring contraction products but reduces the yields of methylcyclohexane and methylcyclohexanone, because of the increased acid functionality and diffusion constraints of intermediates. A low BAS/Pt ratio is beneficial for improving catalytic stability by reducing coke deposition.

Enhanced Antioxidation Stability of Iron-Based Catalysts via Surface Decoration with ppm Platinum

Enhanced stability of iron-based catalysts by noble metals has been previously reported. To further understand the efficiency of precious metals in preventing the Fe surface from being oxidized, we synthesized a series of Pt-doped Fe catalysts with controlled amounts of Pt decoration on the Fe surface using one-pot hydrolysis and co-condensation of inorganic salts, which were then studied in the hydrodeoxygenation (HDO) of m-cresol. The results showed that the addition of Pt could significantly improve the catalyst activity and stability in the HDO of m-cresol. A minimum Pt/Fe atomic ratio of 1/13 was found to maintain the Fe stability, implying that Pt has an ensembled effect on Fe or Pt atoms to stabilize neighboring Fe atoms. In particular, a 0.05Pt–Fe catalyst with a trace amount of Pt (50 ppm or 0.05 wt % Pt) showed excellent stability without oxidation for 40 h time-on-stream even in the presence of H2O. This work illustrates that the activity and stability of earth abundant Fe-based catalysts can b...

Hydrodeoxygenation of m-cresol over bimetallic NiFe alloys: Kinetics and thermodynamics insight into reaction mechanism

Developing mechanistic insights into the reaction network of hydrodeoxygenation (HDO) of lignin-derived compounds is key to rational design of high-performance catalysts for bio-oils upgrading. Herein, we present a comprehensive theoretical study on HDO of m-cresol, a model compound of phenolics, on Ni(1 1 1) and NiFe(1 1 1) surfaces using periodic density functional theory calculations and microkinetic modeling techniques, with a focus on the several competing reaction pathways including enol-keto tautomerization, hydrogenation, and dehydroxylation. Our results show that the activation of the COH bond of m-cresol and phenolic intermediates can be greatly promoted on oxophilic NiFe(1 1 1), evidenced by the elongated COH bond length and the enhanced dehydroxylation activity with respect to Ni(1 1 1). It is found that m-cresol HDO on NiFe(1 1 1) shares certain common features with that on Ni(1 1 1), but exhibits important differences that result in dramatic changes in selectivity. We show that the COH bond length of adsorbed phenolic intermediates can be used as a good descriptor for prediction on the COH bond scission reaction in HDO. Finally, microkinetic modeling augmented by degree of rate control analysis is applied to rationalize the experimentally-observed differences in product distributions over Ni and NiFe catalysts when kinetic factors still dominate.

Hydrodeoxygenation of m-cresol over nickel and nickel phosphide based catalysts. Influence of the nature of the active phase and the support

The present work studied the effect of two supports (SiO2 and tetragonal ZrO2) on the performance of metallic nickel and nickel phosphide catalysts for the hydrodeoxygenation (HDO) of m-cresol carried out at 340°C under 4MPa. All catalysts were characterized using several techniques (ICP, N2 adsorption-desorption, XRD, H2-TPR, NH3-TPD). The active phases (Ni(0) and Ni2P) were successively prepared at 450°C under 4MPa of H2, as observed by XRD. The activity and deoxygenation properties depended on the active phase (Ni vs Ni2P) and the support (SiO2 vs ZrO2). The order of HDO activity (mmolg−1h−1) followed: Ni2P/ZrO2 (47.0)>Ni2P/SiO2 (28.3)>>Ni/ZrO2 (3.0)>Ni/SiO2 (1.1). The Ni2P phase was clearly much more active than metallic Ni. In addition, the use of zirconia as support enhanced the deoxygenation properties compared to silica, which can be attributed to the presence of oxophilic sites (Zr3+/Zr4+) favoring the adsorption of m-cresol.

Effect of the support on the hydrodeoxygenation of m-cresol over molybdenum oxide based catalysts

The hydrodeoxygenation (HDO) of m-cresol was investigated over supported molybdenum oxide catalysts at 340°C under 4MPa as total pressure. All catalysts were fully characterized using several techniques such as atomic absorption, N2 physisorption, XRD, H2-TPR, NH3-TPD, Raman spectroscopy, TEM analysis and oxygen chemisorption. It was noted that the reducibility of molybdenum species depends on the support used and follows the same order than the one determined from the HDO activity, i.e. MoOx/Al2O3>MoOx/SBA–15>MoOx/SiO2. In addition, the use of an ordered mesoporous silica support (SBA-5) or an acidic support (Al2O3) favored significantly the dispersion of MoOx particles compared to SiO2.Under these experimental conditions, m-cresol transformation underwent through two parallel deoxygenation routes which involved either the direct CO bond scission leading to toluene (DDO route), or the total hydrogenation of the aromatic ring yielding mainly to a mixture of methylcyclohexene isomers (HYD route). Regardless of the support used, the DDO route was always predominant. A reaction mechanism was proposed to explain the formation of toluene, the main product observed from HDO of m-cresol. To explain the formation of this aromatic, a selective adsorption through the oxygen atom of the phenolic reactant on oxygen vacancies, acting as HDO active sites, was proposed.

Vapor phase hydrodeoxygenation and hydrogenation of m-cresol on silica supported Ni, Pd and Pt catalysts

Hydrodeoxygenation of m-cresol (a model compound of lignin derived phenolics in bio-oil) has been studied on silica supported Ni, Pd and Pt catalysts at 250°C and atmospheric pressure. Hydrogenation (to 3-methylcyclohexanone and 3-methylcyclohexanol) and hydrodeoxygenation (to toluene) are the primary reactions over all catalysts. The intrinsic hydrogenation activity follows the order of Ni<Pd<Pt, and the deoxygenation activity follows the order of Ni≪Pd≈Pt. The oxygen removal is mainly through a direct deoxygenation (DDO) route. The hydrogenation–deoxygenation (HYD) route is not important due to the lack of acidic sites to catalyze dehydration and a rather low hydrogenolysis activity of the C–OH bond of 3-methylcyclohexanol. At high conversions, the initial hydrogenation products are reversely dehydrogenated to m-cresol, making the deoxygenation to toluene and its subsequent hydrogenation to methylcyclohexane the major pathway. In general, increasing reaction temperature suppresses the hydrogenation reaction but promotes the hydrodeoxygenation as well as C–C bond hydrogenolysis. On Pd and Pt, increasing temperature improves deoxygenation to toluene over the C–C bond hydrogenolysis. In contrast, higher temperature favors the successive C–C hydrogenolysis to produce the low value methane on Ni.

Hydrodeoxygenation of m-cresol with Pt supported over mild acid materials

The deoxygenation of m-cresol was studied using Pt catalysts supported on different materials of various levels of acidity, such as gamma alumina, silica, and H-BEA zeolites. The reaction was carried out at atmospheric pressure and 300°C in a fixed-bed reactor. The catalysts were characterized by XRD, BET, TPR, TEM, H2 and CO chemisorptions, pyridine-TPD and pyridine-IR. The (metal function/acid function) ratio and the reaction conditions were adjusted in order to have a high selectivity to toluene. The effects of acid sites density, strength and type, as well as the pore structure of the different supports on the deoxygenation activity, selectivity and stability were addressed. In order to avoid the production of heavy products and a fast deactivation, the concentration of Brønsted acid sites must be very low. A high acid sites density is detrimental for catalyst stability, due to coke formation via condensation of precursors adsorbed on adjacent sites. Additionally, a mesoporous structure is better than a microporous structure regarding the stability. All the catalysts can be regenerated in air at relatively low temperature.