Catalytic Hydrodeoxygenation Of Guaiacol Research Articles

Catalytic hydrodeoxygenation of guaiacol as a model compound of woody bio-oil over Fe/AC and Ni/γ-Al2O3 catalysts

In this study, Ni/γ-Al2O3 and Fe/activated carbon (AC) catalysts were prepared by an incipient impregnation method and then utilized for hydrodeoxygenation (HDO) of guaiacol (GUA). The AC used in the process was derived from bamboo through steam activation. The effects of the calcination temperature, metal loading, and phosphorus addition on the HDO of GUA were systematically investigated. At 300 °C and atmospheric pressure, 91.52% of GUA was successfully transformed into cresol and 1,2-dimethoxybenzene in liquid phase using 10 wt% of the Fe/AC catalyst, which was calcined at 550 °C. Under the same reaction conditions, utilizing 10 wt% of the Ni/γ-Al2O3 catalyst, which was calcined at 450 °C, resulted in 96.88% GUA conversion, producing 13.03% of cresol, 58.98% of 1,2-dimethoxybenzene, and 27.99% of 3-methyl guaiacol. Additionally, the reaction pathways of the GUA HDO were proposed based on the obtained product distributions.

Hydrodeoxygenation of guaiacol over Ni2P/SiO2–reaction mechanism and catalyst deactivation

The catalytic hydrodeoxygenation of guaiacol, a phenolic model compound of biomass lignin pyrolysis products, has been investigated under atmospheric pressure in H2 utilizing a Ni2P/SiO2 catalyst. Reaction networks are proposed based on the product distribution as a function of contact time and the temperature programmed surface reaction of adsorbed guaiacol and anisole. Guaiacol is mainly converted to benzene through demethoxylation and dehydroxylation via phenol and anisole as intermediates. Demethylation of guaiacol is a side-reaction, which produces small amounts of catechol. Spent catalyst samples were characterized by means of XRD, XPS, TEM, and temperature programmed oxidation to gain understanding the observed slight deactivation. Coke deposition, sintering, and the altering properties of Ni and P species on catalyst surface all contribute to deactivation, while there is no indication of surface oxidation after reaction. The increase of Niδ+ or Ni0 on the Ni2P surface and the decrease of Brønsted acid sites (i.e. POH) are considered to be the major reasons of product distribution changes.

Catalytic Hydrodeoxygenation of Guaiacol over Palladium Catalyst on Different Titania Supports

Pd catalysts supported on TiO2 with different crystalline phases were prepared with formaldehyde as reducing agent and examined for hydrodeoxygenation (HDO) of guaiacol. Their properties were characterized by N2 adsorption, X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. Compared to the carbon-supported Pd catalysts, TiO2-supported Pd catalysts exhibited higher C–O bond scission ability, which may be attributed to the presence of partially reduced titanium species originating from the reduction of Ti4+ by spillover hydrogen from Pd at 200 °C on the surface of TiO2. Guaiacol was hydrogenated on Pd sites to give 2-methoxycyclohexanol, which diffused to partially reduced titanium species and subsequently reacted with hydrogen from Pd to generate cyclohexane. Anatase TiO2-supported Pd catalyst gave the highest HDO activity of guaiacol among the Pd catalysts supported on three types of TiO2 (anatase, rutile, and their mix, P25), suggesting that more partially reduced ...

Catalytic Hydrodeoxygenation of Guaiacol as Lignin Model Component Using Ni-Mo/TiO2 and Ni-V/TiO2 Catalysts

Catalytic hydrodeoxygenation of guaiacol (2-methoxy phenol), an oxygen rich lignin model compound, has been investigated aiming at the elucidation of active catalysts for production of deoxygenated products. All catalysts were synthesized by impregnation technique. Screening of different catalysts unveiled Ni-Mo/TiO2 as the most active catalyst. Ni-Mo/TiO2 was compared with Ni-V/TiO2 to understand the influence of promoter (Mo and V); nevertheless, Ni-V/TiO2 produced no positive effect compared to Ni-Mo/TiO2. Structural investigation was performed using XRD, TEM, BET surface area and TPD measurements. As evidenced by XRD and TEM, all catalysts composed of nano-sized particles. Ni-Mo/TiO2 showed small sized finely dispersed particles, on the other hand large particles and loss of dispersion noted for Ni-V/TiO2 and Ni/TiO2, respectively. BET surface area measurement depicted Ni-Mo/TiO2 catalyst presented high surface area with optimal mesopores than Ni-V/TiO2. The NH3-TPD data revealed that Ni-Mo/TiO2 acidic strength is higher than the Ni-V/TiO2. Influence of catalysts and reaction variables were investigated using both Ni-Mo/TiO2 and Ni-V/TiO2 to determine their potential role on guaiacol conversion. High activity of Ni-Mo/TiO2 during wide range of conditions could be attributed to: (i) small sized and finely dispersed active metal particles, (ii) more mesopores, and (iii) high acidic strength. Water as a solvent, showed no impact on Ni-V/TiO2 performance, while on Ni-Mo/TiO2, guaiacol conversion and phenol selectivity inclined to decrease.

Catalytic hydrodeoxygenation of guaiacol over platinum supported on metal oxides and zeolites

Hydrodeoxygenation of guaiacol over Pt-based catalysts was studied as a representative for phenolic compounds in pyrolysis oil. Screening of various Pt-based catalysts supported on different oxides and using different preparation methods resulted in 1% Pt/SiO2 and platinum supported on zeolites, such as 1% Pt/H-MFI-90, as the most promising catalysts in a temperature range up to 200°C. Thereby conversions of 86 % and 100 % were received, respectively. Particularly, selectivities to cyclohexane above 90 % were achieved for 1% Pt/H-MFI-90.X-ray absorption near edge structure (XANES) uncovered that mild reduction temperatures were sufficient for the reduction of 1% Pt/SiO2 (up to 150°C) and 1% Pt/H-MFI-90 (up to 40°C) while 1%Pt/Al2O3 required a higher temperature of at least 320°C. The average particle size obtained for Pt/SiO2 was 2–3nm as unraveled by scanning transmission electron microscopy (STEM) and extended X-ray absorption fine structure (EXAFS). The deoxygenation ability of the catalysts was improved if the Pt particles were deposited on an acidic H-MFI zeolite (>130μmol acid sites per gram) as support. 1% Pt/SiO2 showed the highest selectivity towards deoxygenation at 50°C, whereas for 1% Pt/H-MFI-90 temperatures of about 150°C were required to achieve a high selectivity to cyclohexane. For the latter catalyst a longer reaction time was beneficial to maximize the selectivity towards cyclohexane. The hydrogen pressure did not have significant influence on the reaction rate. The results are in agreement with a hydrodeoxygenation mechanism over Pt/zeolite catalysts at temperatures up to 200°C that comprises hydrogenation in the first step and acid catalyzed dehydration combined with hydrogenation in the second step.

Catalytic Hydrodeoxygenation of Guaiacol on Rh-Based and Sulfided CoMo and NiMo Catalysts

This study investigates the hydrodeoxygenation (HDO) of guaiacol (GUA), a lignin model compound, using two types of catalysts: mono- and bimetallic Rh-based catalysts and classical sulfided CoMo and NiMo catalysts. The former exhibited greater reactivity than the latter. However, substituting some of the Rh ions with another noble metal (i.e., Pd or Pt) produced no positive effect. This study also proposed the mechanisms of GUA HDO for both types of catalysts. The first step of Rh-based catalysts was hydrogenation of GUA's benzene ring, followed by demethoxylation and dehydroxylation. As for the sulfided CoMo and NiMo catalysts, GUA HDO began with demethylation, demethoxylation, and deoxygenation, followed by benzene ring saturation. A better understanding of HDO surface chemistry may lead to more efficient catalysts for target products.