(206e) Effect of Adsorption of CO2 and H2 on Methanation Reaction By Ni/Al2O3

In an attempt to study the reaction mechanism for recycling carbon dioxide to methane over Ni-Al₂O₃ catalyst, effect of adsorption of both CO₂ and H₂ was studied and their competitive uptake was investigated. Single and multicomponent adsorption experiments for both gases by 18 wt.% Ni doped onto -Al₂O₃ were conducted by using Gravimetric analysis technique.

Adsorption isotherms showed a linear coverage for H₂ onto the catalyst surface, and multilayers isotherm for CO₂ with a mono-saturation capacity of 10.2 mg CO₂/g. Multicomponent adsorption isotherm showed a total uptake of 17.8 mg/g for both gases obtained at 230 ^oC, total pressure of 30 bars and initial H₂/CO₂ molar ratio of 4:1. Ideal Adsorption Theory calculation (IAS) was used to predict the individual uptake and showed that increasing total pressure above 7 bars lead to decreasing the ratio of H₂/CO₂ uptake, that affected the selectivity of methane production.

Consequently, at reaction conditions of 230 ^oC, 7 bars, GASV of 6000 ml/g.h and H₂/CO₂ ratio of 4:1, the conversion of CO₂ was 89% with 100% selectivity to CH₄. Increasing GHSV resulted in decreasing the conversion to reach a value of 70.3% at 36,000 ml/g.h.

Synthesis of CH₄ from recycling of CO₂ is directly affected by adsorption of the reacted gases. The resistant of adsorption/desorption steps will be future investigated and compared to surface reaction one.