No abstract

Catalytic hydrolysis is considered an effective strategy for treating carbonyl sulfide (COS)�a toxic sulfurcontaining gas that causes problems to the environment and petrochemical industries. Al 2 O 3 -based materials are commonly used as catalysts for COS hydrolysis owing to their stability and cost effectiveness. However, they still suffer from sulfur poisoning leading to partial COS conversion after long time use. To improve their catalytic performances, herein, we computationally designed and studied the catalytic activity of the Pt-supported Al 2 O 3 catalysts by means of density functional calculations. We mechanistically explored the COS hydrolysis on both bare and Pt-decorated surfaces to reveal the role of Pt catalysts in the reaction kinetics. We find that bare Al 2 O 3 suffers from difficult C− S bond breaking as its barrier is relatively high. Pt facilitates C−S bond breaking where its barrier is reduced by more than half (1.34 to 0.60 eV). However, the Pt−Al 2 O 3 catalyst could encounter sulfur poisoning as the sulfur-containing intermediates are rather stable. Such issues could be remedied by increasing the operating temperature to destabilize the intermediates and promote product desorption. The energetic span models reveal that the important states of bare and Pt−Al 2 O 3 are indeed C−S bond breaking and product desorption corresponding to an energy span of 2.72 and 1.67 eV at 773 K, respectively�suggesting that Pt dramatically enhances the catalytic activity of Al 2 O 3 -based catalysts toward COS hydrolysis. The suggested operating temperatures are above 673 K to avoid sulfur poisoning. Our findings will be useful for the development of more efficient Al 2 O 3 -based catalysts for treating COS.

Vinasse, a sugar-ethanol residue, is used as a substrate for biogas production. The characteristics of the vinasse wastewater used were 216,000 mg-COD/L, pH 4.1, and 68.42 mg/L volatile solids. The sludge/wastewater ratio was controlled at about 1.5−2.0, by weight. Biogas production enhancement was studied in relation to two parameters – Citadel BioCat + , a commercial biocatalyst containing a large microorganism population as the methanogenic bacteria source (5 and 10 g), and reaction temparature (30 and 37 °C). Biogas production kinetics were evaluated. The presence of the biocatalyst enhanced biogas production significantly, as well as reducing the time required for anaerobic digestion. The first-order kinetic model described the biodegradation process. The best results were found using 10 g of biocatalyst at 37 °C – i.e., the optimum results based on biogas production potential (A), the highest biogas production rate (U), the minimum biogas production time (λ), and kinetic organic biodegradability constants (k) of 102.71 mL/g-COD, 11.17 mL/g-COD/d, 0.95 day, and 0.0533 day − 1, respectively. COD removal efficiency was up to 60%.

The removal of contaminated HCl gas in the petrochemical plants is essential to prevent corrosion problems, catalysts poisoning, and downstream contamination. Alkali-treated activated carbon (AC) was proposed as an effective adsorbent for HCl removal. Understanding the underlying mechanism of HCl adsorption on modified AC is key to design promising strategies for removal of HCl and other chlorinated hydrocarbon gases in the H2 feedstock. Here, a combined experimental and computational approach was used to study the role of alkali treatment on the adsorption behavior of HCl on the AC surfaces. We find that an interplay between alkali ions and oxygen-containing functional groups on the AC surface plays a crucial role in stabilizing the adsorbed HCl. The origin of such stable adsorbed configurations can be attributed to the dissociative adsorption of HCl leading to a formation of low energy species such as water, OH– and Cl– anions. These anions are electrostatically stabilized by the alkali ions resulting in a strong adsorption of −3.61 eV and −3.69 eV for Na+ and K+, respectively. Close investigation on charge analysis reveals that the epoxy functional group facilitates adsorbent-surface charge transfer where O and Cl atoms gain more charges of 0.37 e and 0.58 e which is in good correlation with the improved adsorption strength. The calculated results are consistence with the experimental observations that the Langmuir adsorptivity has been enhanced upon alkali modification. The maximum adsorption capacity of AC has been improved approximately by 4 times from 78.9 to 188.9 mg/g upon treatment.