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Kinetics of toluene hydrogenation—integrating a dynamic approach regarding catalyst activity

“…Such compounds, if present, are not in the form of coke. This transition in catalyst activity or 'deactivation' is reported by various researchers for toluene hydrogenation over various catalysts [3,9,10,[11][12][13][14][15][16]. Their results represent catalyst activity at time^0 as they used a bracketing technique (i.e.…”

“…A non-dissociative hydrogen adsorption approach is reckoned as if hydrogen adsorbs dissociatively, then it forms strong bonds with the surface of catalyst metal; while according to Gaidai et al [26], the only hydrogen that takes part in the reaction for Pt-based catalysts is loosely bonded. Such behavior is also used to explain the decrease in the hydrogenation rate when the reduction temperature of the catalyst is increased [9,10]. This may lead to hydrogen adsorption as molecules.…”

“…However, the first hydrogen addition to the aromatic ring is also considered to be rate limiting [14] as the resonance energy is higher than that of any single hydrogen addition step [27,28]; the resonance energy is related to the first hydrogen addition or the toluene adsorption. On the other hand, some researchers [9,10,15] concluded the addition of the second hydrogen as rate limiting. Lindfords and Salmi [12] have also considered addition of all six hydrogen atoms as rate determining.…”

“…Rahman and Vannice [15,16] argued that Brønsted acidic sites on the support increase the hydrogenation rate, but after reduction at high temperatures, such sites were removed thus decreasing the activity. According to Gaidai et al [9,10], the strongly bonded hydrogen adsorbed on the surface due to catalyst reduction at high temperature is responsible for the decrease in reaction rate. This is because it decreases the spillover hydrogen responsible for the hydrogenation of toluene adsorbed on the support material.…”

“…Also some studies previewed this molecule as a potential hydrogen storage molecule that may be used in mobile resources [8]. The catalyst chosen to effectuate this reaction is Pt/Al 2 O 3 , as it is a well-known hydrogenation catalyst for toluene with no reported Strong Metal Support Interaction (SMSI) effects [9,10].…”