Title : Exploring reactivity trends and catalyst deactivation in biogas reforming
Biogas obtained from biomass, consisting primarily of methane and carbon dioxide, can be subjected to reforming to produce syngas. An ab initio microkinetic model (MMK) is developed to understand the reactivity trends of the terrace (111) and stepped (211) sites of transition metal catalysts for biogas reforming (BGR) reactions.Obtained results are identifying the dominant reforming route; steam reforming of methane (SRM) or dry reforming of methane (DRM) and the coking propensity. Ni is calculated to show maximum turnovers for methane consumption [Ni ~ 102 s-1] followed by Rh and Pd [1 s-1] over the (111) sites, Fig 1a. However, majority of the methane consumed ends up forming coke [Ni ~ 10 s-1; Rh and Pd ~ 10-1 s-1] leading to catalyst deactivation, Fig 1b. In comparison to Ni, Pd and Rh, the (111) sites of Co and Ru calculated lower turnover of methane [10-1 s-1] and coke formation [< 10-3 s-1]. Moreover, H2/CO ratio obtained on Co and Ru (3 to 4) is observed to be closest to the preferred ratio (2 to 3) in syngas valorisation, Fig 1c. Over the (211) facets, Pt and Co display highest activity for methane consumption (103s-1, Fig 1f). However, coke formation are showing high turnover over Pt [103s-1] and Co [102s-1] catalysts, Fig 1g. In contrast, as compared to Pt and Co, step sites of Ru is showing two order of magnitude lower rate of coke production. In general, on both the catalyst surfaces, H2O and CO2 consumption plots are observed to show lower turnovers as compared to methane consumption on all the active metals studied, indicating that methane is undergoing decomposition to produce coke besides SRM and DRM reactions. Also, step sites are exhibiting higher coking as compared to the terrace sites. Among the two reforming routes, SRM rates are more pronounced than DRM on both the surfaces, suggesting that the dominant reforming route in BGR is SRM (Fig 1d and 1i). From the selectivity analysis, Co and Ru are observed to show similar rates of CO formation and CH4 consumption over the (111) and (211) sites (Fig 1e and 1j). Therefore, Co and Ru are suggested as suitable candidates for developing a BGR catalyst owing to higher rates of reforming and relatively reduced coke deposition as opposed to other metals.
Audience Take Away:
- The audience can understand how the optimum catalysts for a particular process maybe designed computationally.
- The study can potentially aid other researchers in expanding their work by providing solutions in terms of computationally designed catalysts which can form a basis for subsequent studies. It can also form a basis for experimentalists in the selection of catalytic systems to run biogas reforming.
- The kinetic modelling employed in this research can be taught as a part of Reaction Engineering course to understand the interplay of various mechanisms and deactivation catalysis.