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Honeycomb monoliths are carbon-based, ceramic or metallic structures, comprising a significant number of packed, small-in-diameter channels. One of the features associated with the honeycomb monoliths is the demonstrated low pressure drops in processes involving high flow rates. Honeycomb monoliths, with a range of structures, have found increasingly promising applications in various industries. Owing to their physical structures, they keep finding new applications in industrial treatment systems. They are mainly fabricated via two different techniques: extrusion and coating. Monoliths fabricated via each of these techniques demonstrate specific characteristics suitable for a certain number of applications. With the presence of cordierite substrate in the coated monoliths, higher mechanical strength of coated honeycomb monoliths is expected when compared to the integral monoliths. The coated monoliths are suitable when mechanical strength is of importance where the adhesion of the thin layer coating on monoliths is a determining factor in the performance of the entire process. The integral monoliths are most-commonly employed in gas-phase processes rather than liquid phase applications due to their high accessible surface area per total weight (or volume) of the monoliths. Embedding mesoporous carbon coating and nanoparticles into honeycomb monoliths has improved the efficiency of monoliths in comparison to the more conventional preparation methods.

In this study, the efficiency of electrochemical reduction of bicarbonate into formic acid was improved by using a composite electrode made up of tin (Sn), nanodiamond (ND) and carbon nanotube (CNT). In the absence of ND, a compositional ratio of 10/90 (Sn/CNT) demonstrated the highest current density. However, by adding ND in a compositional ratio of 10/90/100 (Sn/CNT/ND) the highest efficiency towards formate/formic acid was achieved. It was observed that the presence of ND enhanced the selectivity of product for formic acid. The effects of bicarbonate concentration and scan rate have also been studied to understand the reduction mechanism. The peak potential shifted towards larger negative values of applied potential with an increase in the scan rate from 0.01 to 0.1 V/s, confirming the irreversible nature of the reduction process. The linear relationship between the current and the square root of the scan rate (with a slope value of 0.519) suggested that the reaction process is fully diffusion-controlled. Formic acid was produced using both electrodes; however, the electrode containing nano-diamond successfully improved the process yield for formic acid. Electrochemical impedance study revealed a significant difference between Warburg coefficient for oxidation and reduction processes with values of 29.63 × 1012 and 67.4 Ω. S−0.5 for the applied potentials of 0.5 V and −0.4 V, respectively. This difference confirmed a low resistance at the electrode/electrolyte interface for the reduction potentials.

Bio-degradable calcined egg-shell/sodium alginate (CES/SA) beads were prepared and functionalized using aqueous ammonia (33%). The tailor-made beads were then used as adsorbent for CO 2 capture in a fixed-bed reactor. The performance of the prepared beads was evaluated under various experimental conditions ( i.e. 1 2 concentration between 20 to 45 vol%). Modification with ammonia could successfully introduce additional functional groups containing nitrogen onto the surface of the CES/SA (up to 10.56 wt%). The results showed an increase in CO 2 adsorption with ammonia-impregnated CES/SA, compared to the non-impregnated CES/SA. A maximum CO 2 adsorption capacity of 0.2380 mmol/g was obtained for the gel beads with 45% CO 2 concentration at 1 bar and 30 °C. The adsorption capacity decreased with an increase in temperature and increased with an elevation in the inlet CO 2 concentration, pressure and flow rate. Among the investigated isotherm models ( i.e. Sips, Freundlich and Toth), the Toth isotherm model best described the adsorption data. The thermodynamic properties using the adsorption isotherm data revealed the entropy change (ΔS > 0) reflected the affinity of the adsorbent with the CO 2 molecules. The CO 2 adsorption/desorption process indicated a drop in the CO 2 adsorption capacity of the gel beads in the second cycle; however, this almost remained constant in the subsequent cycles. This observation pointed out to a chemisorption process for the fresh adsorbent and a physical adsorption mechanism for the subsequent adsorption cycles.