A pinboard by
Andrew Ng Kay Lup

PhD Student, University of Malaya


Optimization of hydrodeoxygenation catalyst through theoretical and experimental kinetic modeling

Hydrodeoxygenation is a chemical process used to reduce oxygen content of bio-oil. Bio-oil is a type of oil harvested from biomass and is potential to be used as transportation fuel. However, bio-oil has high oxygen content due to the large amount of oxygen-containing compounds within it. High oxygen content in fuel is unfavorable as it reduces the energy output and poses corrosion issues within the engine. Thus, hydrodeoxygenation is required for the conversion of bio-oil to high quality fuel. At the heart of this process lies the essential removal of oxygen from the oxygen-containing compounds in bio-oil which are commonly found to be phenolic compounds.

Besides reducing the oxygen content of bio-oil, one of the striking features of hydrodeoxygenation is that it converts phenolic compounds into hydrocarbons which are high-added value and high energy content products. This process is made possible through the use of hydrogen gas and catalyst. The role of catalysts is to reduce the hydrodeoxygenation energy requirement and to speed up the process through various complex chemical interactions with the phenolic compounds and hydrogen.

Therefore, my study in this particular area is to investigate on the chemical interactions of the phenolic compounds and hydrogen with catalyst. Since different catalysts have various interactions in this process, the use of transition metals supported on metal oxides would be the only class of catalysts which I would be investigating on. The understanding of such catalytic interactions will be made qualitatively via catalyst characterization and quantitatively via reaction kinetics analysis.

By conducting catalyst characterization, many chemical and physical properties of catalyst could be revealed. Subsequently, these properties could be determined in their roles to promote or inhibit hydrodeoxygenation. By conducting reaction kinetics analysis, quantitative data such as conversion, yield, selectivity of the reaction itself could be determined. These kinetic parameters are necessary to explain the reaction mechanism of hydrodeoxygenation accurately. Thus, through both of these studies, the understanding of catalyst roles and reaction mechanism could enable an accurate determination of excellent hydrodeoxygenation catalyst which results in high yield of high quality fuel via economical process conditions.


Kinetics of the hydrodeoxygenation of cresol isomers over Ni2P/SiO2: Proposals of nature of deoxygenation active sites based on an experimental study

Abstract: Publication date: 15 May 2017 Source:Applied Catalysis B: Environmental, Volume 205 Author(s): Vinicius O.O. Gonçalves, Priscilla M. de Souza, Victor Teixeira da Silva, Fabio B. Noronha, Frédéric Richard The hydrodeoxygenation of cresols (m-cresol, p-cresol and o-cresol) over Ni2P/SiO2 was carried out between 250 and 340°C under high hydrogen pressure (between 1.6 and 3.2MPa). XRD demonstrated that the desired Ni2P phase was obtained at 450°C using 4MPa of H2. The catalytic behavior of Ni2P/SiO2 for the transformation of cresols indicated that these compounds were deoxygenated by two different pathways, which involved different reactions such as hydrogenolysis, hydrogenation, dehydration and isomerization. Using these experimental conditions, i.e. under hydrogen pressure, the catalyst used exhibited a remarkable stability, at least during 20h. An effect of the position of the methyl group in cresol isomers was highlighted, m-cresol being the most reactive whereas o-cresol the less reactive. In addition, an increase of temperature and hydrogen pressure allowed to ensure a high deoxygenation degree of phenolic reactants even at low level of conversion (less than 20%). The participation of different active sites and adsorption modes were proposed to explain the different products observed and their distribution. Graphical abstract

Pub.: 28 Dec '16, Pinned: 24 Aug '17

Hydrodeoxygenation of Phenol over Pd Catalysts. Effect of Support on Reaction Mechanism and Catalyst Deactivation

Abstract: This work investigates the effect of the type of support (SiO2, Al2O3, TiO2, ZrO2, CeO2, and CeZrO2) on the performance of Pd-based catalysts for the hydrodeoxygenation of phenol at 573 K using a fixed-bed reactor. Product distribution is significantly affected by the type of support. Benzene was the major product over Pd/TiO2 and Pd/ZrO2; on the other hand, cyclohexanone was the main compound over Pd/SiO2, Pd/Al2O3, Pd/CeO2, and Pd/CeZrO2. A reaction mechanism based on the tautomerization of phenol was proposed on the basis of DRIFTS experiments and catalytic tests with the intermediate products. The high selectivity to benzene over Pd/TiO2 and Pd/ZrO2 catalysts is likely due to the oxophilic sites of this support represented by incompletely coordinated Ti4+ and Zr4+ cations in close proximity to the periphery of metal particles. The greater interaction between oxygen in the keto-tautomer intermediate with oxophilic sites promotes the selective hydrogenation of C═O bond. Pd/SiO2, Pd/Al2O3, Pd/TiO2, and Pd/ZrO2 catalysts significantly deactivated during TOS. However, Pd/CeO2 and Pd/CeZrO2 were more stable, and only slight losses in activity were observed. Carbon deposits were not detected by Raman spectroscopy after reaction. DRIFTS experiments under reaction conditions revealed a buildup of phenoxy and intermediate species during reaction. These species remained adsorbed on the Lewis acid sites, blocking those sites and inhibiting further reactant adsorption. The growth of Pd particle size and the reduction in acid site density during HDO of phenol were the primary routes of catalyst deactivation. The higher stability of Pd/CeO2 and Pd/CeZrO2 catalysts is likely due to the higher amount of oxygen vacancies of these supports.

Pub.: 02 Feb '17, Pinned: 24 Aug '17

Highly effective hydrodeoxygenation of guaiacol on Pt/TiO2: Promoter effects

Abstract: This work investigated Mg and Mo effect on the hydrodeoxygenation (HDO) of guaiacol over Pt/TiO2 catalyst. The Pt-based catalysts were prepared by the incipient wetness impregnation technique, and tested at 285 °C and 4 MPa in a fixed bed reactor system. The properties of the catalysts were characterized by CO pulse chemisorption, H2-TPD, NH3-TPD, and XRD. The characterization results reveal that Mg or Mo species on Pt/TiO2 increase Pt dispersion, and reduce the surface acidity of Pt/TiO2. Moreover, Mg species lower the hydrogenolysis activity of Pt/TiO2, while Mo species, on the contrary, activate more hydrogen in the reaction. Both Mg and Mo modified Pt/TiO2 catalyst increase guaiacol conversion from 70% to 94% without catalyst deactivation. Mg does not improve the cyclohexane yield. Instead, more carbonaceous species deposit and even graphitic coke are observed on the catalyst after reactivity test. On the contrary, Mo increases the cyclohexane yield from 23.5% to 57.7% with only more active carbon formation on the catalyst after reactivity test, which indicates the active hydrogen species from metal sites and metal-support interface may play a critical role for deep HDO. For the possible reaction pathways, Mg inhibits dehydration and hydrogenolysis pathway from phenol to cyclohexane. However, Mo species favor hydrogenolysis while suppress dehydration to cyclohexane. Thus, Pt-Mo/TiO2 is a promising catalytic system for HDO, and further optimization of its properties may lead to an effective catalyst for the HDO of real and complex pyrolysis bio-oils.

Pub.: 21 Mar '17, Pinned: 24 Aug '17

Catalytic hydrodeoxygenation of anisole over Re-MoOx/TiO2 and Re-VOx/TiO2 catalysts

Abstract: The hydrodeoxygenation of anisole at 300 °C and 3 MPa H2 in a batch reactor is used as a model reaction to explore the performance of TiO2-supported Re-MoOx and Re-VOx catalysts. The binary catalysts were prepared with different Re and MoOx (or VOx) loadings and characterized by nitrogen physisorption, ICP-MS and AAS, XRD, FTIR, H2-TPR, NH3-TPD, H2-TPD, TEM and XPS techniques. A series of catalysts consisting of a base-metal (Re, Ga, Ni and Co) in combination with reducible metal oxide (Mo and V) were initially screened: due to its oxophilic nature only supported Re catalysts showed the ability to catalyze aromatic C<img border="0" alt="single bond" src="http://cdn.els-cdn.com/sd/entities/sbnd" class="glyphImg">O bonds to produce aromatic hydrocarbons. This capability was enhanced by pairing Re with partially reduced surface MoOx (or VOx) sites, particularly in equimolar proportions. The catalytic activity, expressed as intrinsic reaction rate, was found to rely on the nature of surface Re, Mo and V species: the activity of Re-MoOx/TiO2 catalysts is dominated by exposed Mo5+ sites while that of Re-VOx/TiO2 catalysts is controlled by Re4+ sites. The results also reveal that despite the highest intrinsic activity of Mo5+ sites, they require the presence a specific type of active sites such as Re, in appropriate amount, to enable the enhanced benzene/toluene production.

Pub.: 17 Feb '17, Pinned: 24 Aug '17

In situ hydrodeoxygenation of phenol with liquid hydrogen donor over three supported noble-metal catalysts

Abstract: In situ hydrodeoxygenation of phenol with liquid hydrogen donor over three supported Pd, Pt, and Ru catalysts was investigated. The method of incipient wetness impregnation was used to load the three noble metals on the support of MCM-41, which is a cylindrical mesoporous material with a hierarchical structure. The in situ hydrodeoxygenation of phenol was conducted at 280 °C, under pressures from saturated vapor of solvent and compressed initial N2 with gas products. Among the three catalysts, Ru/MCM-41 was found to be the best one, with highest phenol conversion of 73.9% and deoxygenation degree of 72.2%. The performance of Ru/MCM-41 increased with increasing theoretical loading amount of Ru and with reduction temperature. However, when the reduction temperature reached to 500 °C, or the Ru theoretical loading amount increased to 15 wt%, the activity of Ru/MCM-41 decreased reversely. Through the characterizations by small-angle XRD, wide-angle XRD, H2-TPR, and SEM analysis, the reason for the deteriorated performance of Ru/MCM-41 under high reduction temperature or high Ru loading amount was deduced as the collapse of MCM-41 structure and severe overlaps of Ru atoms. Hydrogen donors were also tested, and formic acid was found in best performance owing to its fast decomposition rate and high productivity of hydrogen. Though an increased feed ratio of formic acid to phenol could improve the hydrodeoxygenation potential of phenol, much simultaneously generated COx from decomposition of formic acid might occupy active sites of the catalyst and led to a decreased growth rate of phenol conversion.

Pub.: 14 Mar '17, Pinned: 24 Aug '17

Structural Properties and Reactivity Trends of Molybdenum Oxide Catalysts Supported on Zirconia for the Hydrodeoxygenation of Anisole

Abstract: A monolayer dispersion of molybdenum oxide gives the highest reactivity for the hydrodeoxygenation and alkylation of anisole, the lignin-derived compound.Vapor-phase hydrodeoxygenation (HDO) of anisole was investigated at 593 K and H2 pressures of ≤1 bar over supported MoO3/ZrO2 catalysts with MoO3 loadings ranging from 1 to 36 wt % (i.e., 0.5–23.8 Mo/nm2). Reactivity studies showed that HDO activity increased proportionally with MoO3 coverage up to a monolayer coverage (∼15 wt %) over the ZrO2 surface. Specific rates declined for catalysts with high loadings exceeding the monolayer coverage, because of a decreasing amount of redox-active species, as confirmed by oxygen chemisorption experiments. For low catalyst loadings (1 and 5 wt %), the selectivities toward fully deoxygenated aromatics were 13 and 24% on a C-mol basis, respectively, while at intermediate and high loadings (10–36 wt %), the selectivity was ∼40%. Post-reaction characterization of the spent catalysts using X-ray diffraction and X-ray photoelectron spectroscopy showed that the catalysts with 25 and 36 wt % MoO3 loadings were over-reduced, as evidenced by the prevalence of Mo4+ and Mo3+ oxidation states summing to 54 and 67%, respectively. In contrast, catalysts with low and intermediate Mo loadings exhibited a prevalence of Mo6+ species (∼60%). We hypothesize that Mo5+ species are more easily stabilized in oligomeric and isolated forms over the zirconia support. The catalysts with intermediate loadings feature HDO and alkylation rates higher than those of catalysts with low loadings because the latter feature a higher proportion of isolated species. Once the monolayer coverage is exceeded, MoO3 crystallites are formed, which can undergo facile reduction to less reactive MoO2.

Pub.: 05 Apr '17, Pinned: 24 Aug '17

Hydrodeoxygenation of Anisole with Pt Catalysts

Abstract: Pt catalysts supported on neutral and acid materials, namely SiO2, γ-Al2O3, Na-Beta, and NaH-Beta, were studied in the anisole deoxygenation reaction. The main objective was to compare different supports for this reaction and determine the conditions that maximize the selectivity to deoxygenated products. The reactions were carried out in a fixed-bed reactor at atmospheric pressure by varying the temperature between 200 and 500 °C. Depending on reaction conditions, benzene, and in lesser amounts toluene and xylenes, were obtained as deoxygenated products. Also, n-methylanisoles and n-methylphenols were produced in low amounts. The effects of space time, temperature, and H2/anisole ratio on the catalytic performance were analyzed in a wide range of values, which thus made it possible to obtain detailed information regarding the changes in selectivity and activity upon changes in the operational variables. Anisole deoxygenation to benzene requires both the metallic and the acid functions. Acid and metal sites promoted demethylation needed to allow the deoxygenation reaction to occur. The acid sites also promote transalkylation reactions, which led to undesired oxygenated products, and on the other hand, the acidity catalyzed the alkylation of aromatic rings with the −CH3 fragments coming from demethylation, thus improving the carbon balance. Coke formation follows a series-type mechanism, formed mainly from the anisole. It is possible to regenerate these catalysts by burning the coke with air at 350–400 °C. The catalysts supported on the beta zeolite worked under a mass transfer controlled regime.

Pub.: 08 May '17, Pinned: 24 Aug '17

Catalysts, Vol. 7, Pages 176: Zirconium Phosphate Heterostructures as Catalyst Support in Hydrodeoxygenation Reactions

Abstract: A porous phosphate heterostructure (PPHs) formed by a layered zirconium(IV) phosphate expanded with silica galleries was prepared presenting a P/Zr molar ratio equal to 2 and a (Si + Zr)/P ratio equal to 3. This pillared zirconium phosphate heterostructure was used as a catalyst support for bi-functional catalysts based on noble metals (Pt or Pd) and molybdenum oxide containing a total metallic loading of 2 wt % and Pt(Pd)/Mo molar ratio equal to 1. The catalysts prepared were characterized by different experimental techniques and evaluated in the hydrodeoxygenation (HDO) reaction of dibenzofuran (DBF) as a model compound present in biomass derived bio-oil, at different reaction pressures. The catalyst characterization evidenced that a high dispersion of the active phase can be achieved by using these materials, as observed from transmission electron microscopy (TEM) characterization, where the presence of small particles in the nanometric scale is noticeable. Moreover, the textural and acidic properties of the phosphate heterostructure are barely affected by the incorporation of metals into its structure. Characterization results evidenced that the presented material is a good candidate to be used as a material support. In both cases, high conversions and high selectivities to deoxygenated compounds were achieved and the active phase played an important role. Thus, Pt/Mo presented a better hydrogenolysis capability, being more selective to O-free products; whereas, Pd/Mo showed a greater hydrogenation ability being more affected by changes in pressure conditions.

Pub.: 02 Jun '17, Pinned: 24 Aug '17

Catalysts, Vol. 7, Pages 169: An Overview on Catalytic Hydrodeoxygenation of Pyrolysis Oil and Its Model Compounds

Abstract: Pyrolysis is considered the most promising way to convert biomass to fuels. Upgrading biomass pyrolysis oil is essential to produce high quality hydrocarbon fuels. Upgrading technologies have been developed for decades, and this review focuses on the hydrodeoxygenation (HDO). In order to declare the need for upgrading, properties of pyrolysis oil are firstly analyzed, and potential analysis methods including some novel methods are proposed. The high oxygen content of bio-oil leads to its undesirable properties, such as chemical instability and a strong tendency to re-polymerize. Acidity, low heating value, high viscosity and water content are not conductive to making bio-oils useful as fuels. Therefore, fast pyrolysis oils should be refined before producing deoxygenated products. After the analysis of pyrolysis oil, the HDO process is reviewed in detail. The HDO of model compounds including phenolics monomers, dimers, furans, carboxylic acids and carbohydrates is summarized to obtain sufficient information in understanding HDO reaction networks and mechanisms. Meanwhile, investigations of model compounds also make sense for screening and designing HDO catalysts. Then, we review the HDO of actual pyrolysis oil with different methods including two-stage treatment, co-feeding solvents and in-situ hydrogenation. The relative merits of each method are also expounded. Finally, HDO catalysts are reviewed in order of time. After the summarization of petroleum derived sulfured catalysts and noble metal catalysts, transitional metal carbide, nitride and phosphide materials are summarized as the new trend for their low cost and high stability. After major progress is reviewed, main problems are summarized and possible solutions are raised.

Pub.: 01 Jun '17, Pinned: 24 Aug '17