Renewable Feedstocks: The Problem of Catalyst Deactivation and its Mitigation

Abstract

Much research has been carried out in the last decade to convert bio-based feedstock into fuels and chemicals. Most of the research focuses on developing active and selective catalysts, with much less attention devoted to their long-term stability. This Review considers the main challenges in long-term catalyst stability, discusses some fundamentals, and presents options for their mitigation. Three main challenges are discussed: catalyst fouling, catalyst poisoning, and catalyst destruction. Fouling is generally related to the deposition of insoluble components present in the feed or formed by degradation of the feed or intermediates. Poisoning is related to the deposition of electropositive contaminants (e.g. alkali and alkaline earth metals) on acid sites or of electronegative contaminants (e.g. N and S) at hydrogenation sites. Catalyst destruction results from the thermodynamic instability of most oxidic supports, solid acids/bases, and hydrogenation functions under hydrothermal conditions.

Hydrogenation of levulinic acid to γ-valerolactone over anatase-supported Ru catalysts: Effect of catalyst synthesis protocols on activity

“…It is recognized as an important carbohydratederived renewable platform molecule and has attracted considerable interest from a number of chemical companies [1,2]. The family of LA derivatives is large and some have much potential for commercialization.…”

“…Al 2 O 3 and SiO 2 , the stability under hydrothermal, acidic conditions is known to be limited, which is of relevance for LA hydrogenations carried out in water or at high LA loadings [25,28]. Estimations of oxide support stability in pressurized water at 200°C were recently provided by Lange using Pourbaix diagrams [2]. SiO 2 has the tendency to be converted into silica gel at all pH values, whereas Al 2 O 3 is well-known to convert into boehmite (AlO(OH)) at pH values between 4.5 and 11.5.…”

Catalyst stabilization by stoichiometrically limited layer-by-layer overcoating in liquid media

“…Catalyst deactivation incurs significant costs due to the need for material regeneration and eventual replacement, and therefore has been a major focus in petrochemical research [1]. Reversible deactivation is often due to coverage of the active site by chemical binding (e.g.…”

“…poisoning) or coverage of the active site (e.g. coking) [1,2]. These forms of chemical deactivation can often be reversed by thermal treatment such as calcination with air.…”

“…Such conditions are required because biomass-derived molecules usually have low volatility and are produced by biomass depolymerization or biological transformation in dilute aqueous or solvent streams [4][5][6]. Irreversible deactivation, including by sintering and leaching, tends to be more pronounced in liquid-phase conditions, which makes catalyst stability even more critical [1,2,7].…”