CO sub(2) adsorption and storage over FAU-zeolites for environmental remediation: Understanding the role of oxygen vacancy and promotor loading

Abstract

The CO sub(2) level is rising in the atmosphere and has reached well above 400 ppm. Thus, there is growing concern about increasing CO sub(2) levels in the atmosphere as it is a greenhouse gas, constituting 20-25 percent of total greenhouse gas emissions. CO sub(2) is quite a resilient molecule and is a by-product of any combustion-driven process. The CO sub(2) conversion is a non-spontaneous process due to its strong stability. The IEA and IPCC constantly mandate laws to monitor and regulate CO sub(2) emissions in the atmosphere. One efficient way is to scrub off CO sub(2) coming out of the exhaust. Several technologies have been developed around this concept, like adsorption and absorption. In this work, we have used zeolite for CO sub(2) adsorption. Four different zeolites with a Si/Al ratio of one, which possess varied pore diameters of 3 Angstrom, 4 Angstrom, 5 Angstrom and 10 Angstrom are tested for CO sub(2) adsorption. The zeolite with the pore diameter of 5 Angstrom exhibited the best performance, which adsorbed 0.3 mmol/g (13.203 mg/g) of CO sub(2). The adsorption capacity of zeolites is further enhanced by creating oxygen vacant sites and loading sodium (Na) promotor. The creation of oxygen vacancy approx. 11 percent for MZE600 sample raises the CO sub(2) adsorption by 1.6 times compared to the ZE. Various concentrations of Na promotor are loaded on zeolite namely 5,10,15,20,25,35 percent. About 11.97 mmol/g (527 mg/g) of CO sub(2) adsorption was observed for 25 percent loading of Na promotor on zeolite (M25NaZE). With the sequential increase in promotor loading (up to 25 percent), CO sub(2) adsorption increases. Further increase in loading reduces the CO sub(2) adsorption, attributed to blockage of pores on sorbent and plausible agglomeration of the promotor. The M25NaZE sample is stable for a minimum of 10 regeneration cycles and exhibits linear response to variation in CO sub(2) concentration from 2.5 percent to 16 percent and feed flow rate of 50-500 mL/min.