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Although multistage thermal decomposition (fractionation) of biomass with catalytic upgrading is a promising strategy of achieving sustainable fuels production, the number of thermal decomposition stages, their conditions, and the optimal catalytic upgrading chemistries are not known. In this paper, we use conceptual process modeling to propose a general roadmap for the design of a biorefinery by employing these technologies. The overall process considered includes a biomass pretreatment system, a (multistage) thermal decomposition system in which the biomass in decomposed into various fractions, a fraction upgrading system, and a combustion system. We focus primarily on the design of the thermal decomposition and fraction upgrading systems. The goal of our work is to demonstrate the key trade‐offs between various process options and to identify important areas for improvement. In general, increasing the complexity of the fraction upgrading systems increases the ultimate yield of C6+ products, though there are diminishing returns on the increase in product yield versus the complexity of the catalytic upgrading sequences. The choice of the number of thermal decomposition stages is not simple and requires careful consideration of the chemistries available to upgrade different components and the relative abundances of these different components. Therefore, the optimal design of the thermal decomposition and fraction upgrading systems cannot be done independently.

Experimental and theoretical studies of hydrodeoxygenation (HDO) of m-cresol show that on metals of low oxophilicity, such as Pt or Pd, the direct CeO bond cleavage is not possible. Therefore, HDO requires an indirect pathway via tautomerization. In contrast, on metals of higher oxophilicity, such as Ru or Rh, the direct CeO bond cleavage is possible and toluene can be directly obtained from m-cresol. These studies show that the HDO activity correlates directly with the metal oxophilicity, which in turn depends on the position of the d-band center relative to the Fermi level. This catalytic descriptor depends on (1) the type of metal and (2) the extent of coordination of the metal atoms. The present contribution investigates the effect of the second factor. It is demonstrated that a Rh/SiO 2 catalyst with small particles (low-coordination sites) is more active for HDO than one with larger particles (high-coordination sites). At the same time, the low coordination site is more prone to deactivation and loss of HDO selectivity. These experimental results are combined with the density functional theory calculations, which show that the energy barrier for direct CeO bond cleavage is lower on a step site than on a terrace site. At the same time, it is shown that a step site requires a higher energy barrier to remove adsorbed molecular fragments to regenerate the activity than a terrace site, which explains the faster deactivation rate observed on catalysts with small more defective metal clusters.

Acylation is an effective C-C bond-forming reaction to condense acetic acid and lignin-derived aromatic compounds into acetophenones, valuable precursors to fuels and chemicals. However, acetic acid is intrinsically an ineffective acylating agent. Here, we report that its acylation activity can be greatly enhanced by forming intermediate aromatic esters directly derived from acetic acid and phenolic compounds. Additionally, the acylation reaction was studied in the liquid phase over acid zeolites and was found to happen in two steps: 1) formation of an acylium ion and 2) C-C bond formation between the acylium ion and the aromatic substrate. Each of these steps may be rate-limiting, depending on the type of acylating agent and the aromatic substrate. Oxygen-containing substituents, such as -OH and -OCH , can activate aromatic substrates for step 2, with -OH> -OCH , whereas alkyl substituent -R cannot. At the same time, aromatic esters can rearrange to acetophenones by both an intramolecular pathway and, preferentially, an intermolecular one.

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