Abstract
Greenhouse gases, chiefly carbon dioxide (CO2) and methane (CH4), emission is responsible for the global warming and heat waves which strike the world causing floods and droughts everywhere with more CO2 attributions. The adsorption and desorption capacities of CO2 and CH4 at room temperature and up to 5.0 and 100 bar, respectively, were investigated for the untreated and ammonia-treated activated carbons (ACs), metal-anchored (metal: Ru, Rh, Pd, Ir or Ni) samples. We merged ammonia treatment and metal decoration to discover their influences on the CO2 and CH4 storage capability of ACs and the potential use of such modified ACs for capturing greenhouse gases and purifying natural gas from CO2. The CO2 storage capacities ranged between 25.2 and 27.7 wt% at 5.0 bar with complete regeneration upon desorption, while the uptakes for CH4 were in the range of 9.6 - 12.6 wt% at 35 bar with hysteresis behavior of the adsorbed gas. The highest adsorption capacities were achieved for the pristine samples, showing that metal decoration reduced slightly the adsorption. Ammonia-treated samples showed minor enhancing effect on the CH4 adsorption in comparison to the CO2 adsorption. The higher adsorption capacities of CO2 than those of CH4 could be employed for upgrading the natural gas, while the 9.6 wt% (2.2 mmol g(-1)) CO2 storage capacity would allow for its removal from the flue gases at ambient temperature and pressure. The higher adsorption capacity and preferentiality of CO2 over CH4 could be attributed mainly to its higher quadrupole moment and its higher clustering above the AC surfaces, while a minor effect, if any, would be attributed to the modifications of the ACs, implying that physisorption mechanism acted significantly in the adsorption process in comparison to chemisorption mechanism at the studied conditions.