Eleni Heracleous

Catalysis meets nonthermal separation for the production of (alkyl)phenols and hydrocarbons from pyrolysis oil.

A simple and efficient hydrodeoxygenation strategy is described to selectively generate and separate high-value alkylphenols from pyrolysis bio-oil, produced directly from lignocellulosic biomass. The overall process is efficient and only requires low pressures of hydrogen gas (5u2005bar). Initially, an investigation using model compounds indicates that MoCx /C is a promising catalyst for targeted hydrodeoxygenation, enabling selective retention of the desired Ar-OH substituents. By applying this procedure to pyrolysis bio-oil, the primary products (phenol/4-alkylphenols and hydrocarbons) are easily separable from each other by short-path column chromatography, serving as potential valuable feedstocks for industry. The strategy requires no prior fractionation of the lignocellulosic biomass, no further synthetic steps, and no input of additional (e.g., petrochemical) platform molecules.

Transition metal promoted K/Mo2C as efficient catalysts for CO hydrogenation to higher alcohols

This study investigates the effect of transition metal promotion in a series of K/Mo2C catalysts doped with Ni, Cu and Mn for the hydrogenation of CO to higher alcohols. The catalysts were found to produce a significant amount of higher alcohols, consisting mainly of linear alcohols with two to four carbon atoms, at mild reaction conditions (temperature of 280 °C and pressure of 40–60 bar). All transition metals increased the selectivity for higher alcohols compared to the reference material. Nickel had the most favorable effect, as it greatly increased CO conversion as well. XPS results revealed a strong interaction between molybdenum in the carbidic phase and the transition metals, indicative of electron transfer from the dopants to the Mo atoms. In the Ni/K/Mo2C catalyst, the formation of a mixed Ni–Mo carbidic phase was evidenced. We postulate that this phase serves as the active centre for non-dissociative CO chemisorption and leads, in combination with dissociative CO adsorption on the Mo2C sites, to higher alcohol formation. Overall, the Ni/K/Mo2C catalyst exhibited the highest catalytic activity, with 23.2% CO conversion, 30.5% higher alcohol selectivity and space time yield to oxygenates of 147.4 mg gcatalyst−1 h−1 at 280 °C and 60 bar. Stability testing of the optimum catalyst for 400 hours time on stream demonstrated considerable deactivation, with an activity decrease of ~48%. The reduction in reactivity can be ascribed to the segregation of the mixed Ni–Mo carbidic phase and the formation of hydrated oxidic nickel species together with a well-defined K2Mo2O7 phase.

On the Mn promoted synthesis of higher alcohols over Cu derived ternary catalysts

This work provides insight into the promotional effect of Mn on the synthesis of higher alcohols over Cu-based ternary catalysts through XPS and in situ DRIFTS and powder XRD. These revealed that the surface of K-CuZnAl, an active catalyst for CO hydrogenation to methanol, possesses Cu+ sites able to adsorb CO associatively and Cu0 sites for H2 dissociation. Here we show that exchanging Zn with Mn induces a strong interaction between Cu and Mn that decreases the overall copper surface area and increases the Cu+/Cu0 ratio. In situ DRIFTS showed that electronic modification of Cu+ sites by proximate Mn favors dissociative CO chemisorption, resulting in the formation of C and O adspecies that are precursors to higher alcohol formation. The decrease in metallic copper limits available sites for H2 dissociation, and hence retards the hydrogenation of oxygen-containing intermediates, thereby further promoting carbon-chain growth. Mn also increases the dispersion of the K promoter over the catalyst surface, providing abundant basic sites for aldol-type condensation reactions to branched oxygenates.

Impact of macroporosity on catalytic upgrading of fast pyrolysis bio-oil by esterification over silica sulfonic acids

Abstract Fast pyrolysis bio‐oils possess unfavorable physicochemical properties and poor stability, in large part, owing to the presence of carboxylic acids, which hinders their use as biofuels. Catalytic esterification offers an atom‐ and energy‐efficient route to upgrade pyrolysis bio‐oils. Propyl sulfonic acid (PrSO3H) silicas are active for carboxylic acid esterification but suffer mass‐transport limitations for bulky substrates. The incorporation of macropores (200u2005nm) enhances the activity of mesoporous SBA‐15 architectures (post‐functionalized by hydrothermal saline‐promoted grafting) for the esterification of linear carboxylic acids, with the magnitude of the turnover frequency (TOF) enhancement increasing with carboxylic acid chain length from 5u2009% (C3) to 110u2009% (C12). Macroporous–mesoporous PrSO3H/SBA‐15 also provides a two‐fold TOF enhancement over its mesoporous analogue for the esterification of a real, thermal fast‐pyrolysis bio‐oil derived from woodchips. The total acid number was reduced by 57u2009%, as determined by GC×GC–time‐of‐flight mass spectrometry (GC×GC–ToFMS), which indicated ester and ether formation accompanying the loss of acid, phenolic, aldehyde, and ketone components.

Effect of the structure and mesoporosity in Ni/zeolite catalysts for the hydroisomerization/hydrocracking of n-hexadecane

The hydroisomerisation/hydrocracking properties of Ni‐zeolite catalysts (H‐MFI and H‐Beta) are studied using n‐hexadecane as model compound and compared with those of Ni/ASA (amorphous silica‐alumina) as reference catalyst. In the case of H‐Beta, the effect of the introduction of mesoporosity by controlled desilication is also investigated. The results indicate that Ni on desilicated H‐Beta catalysts shows very interesting characteristics for the potential use in the production of biofuel from vegetable/algal oil, or the upgrading of biomass‐derived Fischer–Tropsch waxes. Ni/H‐Beta shows lower activity with respect to Ni/H‐MFI, but significantly lower formation of gases and much better hydroisomerisation activity. The introduction of mesoporosity by desilication enhances the activity, while still maintaining an acceptable gas formation and good hydroisomerisation properties. Furthermore, the desilication treatment improves the stability with respect to carbon formation.