Nucleation as a rate-determining step in catalytic gas generation reactions from liquid phase systems

Abstract

The observable reaction rate of heterogeneously catalyzed reactions is known to be limited either by the intrinsic kinetics of the catalytic transformation or by the rate of pore and/or film diffusion. Here, we show that in gas generation reactions from liquid reactants, the nucleation of gas bubbles in the catalyst pore structure represents an additional important rate-limiting step. This is highlighted for the example of catalytic hydrogen release from the liquid organic hydrogen carrier compound perhydro-dibenzyltoluene. A nucleation-inhibited catalytic system produces only dissolved hydrogen with fast saturation of the fluid phase around the active site, while bubble formation enhances mass transfer by more than a factor of 50 in an oscillating reaction regime. Nucleation can be efficiently triggered not only by temperature changes and catalyst surface modification but also by a mechanical stimulus. Our work sheds new light on performance-limiting factors in reactions that are of highest relevance for the future green hydrogen economy.

Performance of Continuous Hydrogen Production from Perhydro Benzyltoluene by Catalytic Distillation and Heat Integration Concepts with a Fuel Cell

“…[ 69,70 ] For the case of hydrogen release from LOHC systems by dehydrogenation, it has been shown that the reaction rate in a state where oscillatory hydrogen bubble nucleation takes place can be up to 50 times higher than a nucleation inhibited state of the same catalyst under otherwise identical conditions. [ 71 ] Moreover, the liquid holdup can influence the residence time in the catalytic section. [ 72,73 ] It is noteworthy that the reaction takes place primarily in the liquid phase, since the catalyst pellets must be wetted to maintain distillation premises.…”

Perspective on Decarbonizing Long-Haul Trucks Using Onboard Dehydrogenation of Liquid Organic Hydrogen Carriers

“…The models for each stage are expected to be considerably varied as a result of different rate-limiting steps. For example, a study by Solymosi et al shows how nucleation to form hydrogen bubbles is the rate-determining step during the initial phases of the startup while not being important during other stages . In addition to optimizing performance, transient analyses are required to establish startup/shutdown protocols and usage guidelines for trucks, which could have practical and economic implications.…”

Closed formula for the transport of micro-nano-particle across model porous media

“…Similarly, understanding the dependence of the flow of water on the porosity of the soil is crucial in environmental sciences [28]. Moreover, diverse techonlogies related to the energy transition such as blue-energy [29], hydrogen technology [30,31], electrolyzers and fuel cells [32,33], or CO 2 segregation [34] rely on the transport of (charged) chemical species across nanoporous materials.…”