Microkinetic modelling and reaction pathway analysis of the steam reforming of ethanol over Ni/SiO2

Abstract

Hydrogen production via the steam reforming of biomass-derived ethanol is a promising environmental alternative to the use of fossil fuels and a means of clean power generation. A microkinetic modelling study of ethanol steam reforming (ESR) on Nickel is presented for the first time and validated with minimal parameter fitting against experimental data collected over a Ni/SiO2 catalyst. The thermodynamically consistent model utilises Transition State Theory and the UBI-QEP method for the determination of kinetic parameters and is able to describe correctly experimental trends across a wide range of conditions. The kinetically controlling reaction steps are predicted to occur in the dehydrogenation pathway of ethanol, with the latter found to proceed primarily via the formation of 1-hydroxyethyl. CC bond cleavage is predicted to take place at the ketene intermediate leading to the formation of CH2 and CO surface species. The latter intermediates proceed to react according to methane steam reforming and water gas shift pathways that are enhanced by the presence of water derived OH species. The experimentally observed negative reaction order for water is explained by the model predictions via surface saturation effects of adsorbed water species. The model results highlight a possible distinction between ethanol decomposition pathways as predicted by DFT calculations on Ni close-packed surfaces and ethanol steam reforming pathways at the broad range of experimental conditions considered.

Elucidation of metal and support effects during ethanol steam reforming over Ni and Rh based catalysts supported on (CeO2)-ZrO2-La2O3

“…This is more noticeable on the TOF plot (Figure 5c), where a clearly negative reaction order in respect to water is obtained for the latter catalysts, whereas on the ceria containing ones the slope is still negative but much closer to zero. Various studies, including our previous work on Ni/SiO2 [25], have suggested that a negative partial reaction order for steam indicates the competitive adsorption of ethanol and water for the same active sites, with the metal surface being gradually saturated by adsorbed water species [63,64]. Clearly, the high oxygen mobility and large oxygen storage capacity of CeO2 allows for an efficient dissociation of steam across its entire surface and a fast delivery of O species to the metal that prevents to a large degree the latter's saturation by steam, as carbon-containing surface intermediates are effectively oxidised.…”

Effect of Supports and Promoters on the Performance of Ni‐Based Catalysts in Ethanol Steam Reforming

“…The reaction pathways and the side reactions of ESR have been well discussed in several books and reviews , . The main point of designing good catalysts is to enhance the main reactions in the ESR as mentioned in the Introduction, while avoiding the side reactions including ethanol dehydration, reverse water‐gas shift reaction, methanation, and deposition of carbon species as follows: …”

“…The reaction pathways and the side reactions of ESR have been well discussed in several books and reviews [89,[137][138][139][140]. The main point of designing good catalysts is to enhance the main reactions in the ESR as mentioned in the Introduction, while avoiding the side reactions including ethanol dehydration, reverse water-gas shift reaction, methanation, and deposition of carbon species as follows:…”

Process Modeling, Optimization, and Heat Integration of Ethanol Reforming Process for Syngas Production with High H2/CO Ratio

“…CO and H 2 are mainly produced with low water input, while CO 2 and H 2 are mainly produced by high water input. Despite the apparent simplicity of these two reactions, complex simultaneous reactions of ethanol decomposition (Equation (3)), methane steam reforming (Equations (4) and (6)), and water-gas shift (Equation (5)) can occur [14,17]. The heat needed for ethanol steam reforming can be obtained from fuel combustion out of the reaction tube.…”

“…Roychowdhury et al [13] modeled the heat transfer of the ethanol steam-reforming process in a microchannel reactor, which found that the conversion rate can be reached as high as 100% when flue-gas flowing supplies the necessary heat. Afolabi et al [14] established a microkinetic model of ethanol steam reforming over a nickel catalyst, which can correctly describe experimental trends. New concepts of self-sustained electrochemical promotion catalysts for partial oxidation of heavy hydrocarbons were also proposed in References [5,15].…”