Enhanced CO₂ Adsorption Using MgO-Impregnated Activated Carbon: Impact of Preparation Techniques

The development of a facile and sustainable approach to produce magnesium oxide (MgO) activated carbons impregnated through a single-step activation of biochar is reported. In a single-step activation process, biochar is impregnated with 3 and 10 wt % of magnesium salt solutions followed by steam activation. In a two-step method, activated carbon, the product of steam activation of biochar, is impregnated with magnesium salt using the incipient wetness and excess solution impregnation process and calcined. The impacts of activation method, impregnation method, and metal content are evaluated, and the product qualities are compared in terms of porosity and surface chemistry. The sorbents are then used for CO2 capture in low partial pressure of CO2 at 25 and 100 °C from a feed containing 15% CO2 in N2 in a fixed-bed reactor. The incipient wetness of activated carbons results in the highest CO2 uptake (49 mg/g) at 25 °C, while single-step impregnation of biochar with rinsing step yields the largest surface area (760 m2/g) and the second highest CO2 uptake (47 mg/g). The increase in Mg content from 3 to 10 wt % results in the smaller surface area and higher CO2 uptake suggesting that the metal content has a greater impact than porosity and surface area. Rinsing the Mg impregnated activated carbon with water results in the larger surface area and higher CO2 uptake in all samples. Moreover, the CO2 adsorption runs at 100 °C shows a 65% increase using MgO impregnated activated carbon as compared to steam activated carbon indicating that MgO impregnation of activated carbon can overcome the limitation of using nontreated activated carbon at moderate operating temperature of 100 °C and low partial pressure of CO2 of 15 mol %

Enhancing Catalytic Ozonation of Acetone and Toluene in Air Using MnO<i>_x</i>/Al₂O₃ Catalysts at Room Temperature

A series of MnOx/Al2O3 catalysts were synthesized by polyol and dry impregnation methods and calcined in the range of 400–800 °C. The impact of the preparation procedure and calcination temperature was investigated to enhance the catalytic degradation of a single component and binary mixtures of acetone and toluene at room temperature. The polyol method produces catalysts with a higher surface area, smaller cluster size, and lower oxidation state than the impregnation method. The results indicated that the oxidation state of manganese shifted to lower values by increasing the calcination temperature, which had a beneficial influence on the catalytic performance. As calcination temperature increases to 800 °C, the catalyst exhibited excellent catalytic activity in acetone degradation while no significant change was observed in degradation of toluene. In the binary mixture, toluene conversion was promoted whereas the acetone conversion was inhibited. X-ray absorption near-edge structure and extended X-ray absorption fine structure results of the spent catalysts showed that, unlike acetone, toluene altered the local structure of manganese oxides during the reaction. The catalyst was susceptible for the reduction process with toluene due to the accumulation of carbonaceous species resulting from incomplete oxidation of toluene

Selective CO₂ Capture by Activated Carbons: Evaluation of the Effects of Precursors and Pyrolysis Process

Activated carbons are produced from different Canadian waste biomasses including agricultural waste (wheat straw and flax straw), forest residue (sawdust and willow ring), and animal manure (poultry litter). The precursors are carbonized through the fast and slow pyrolysis processes and then activated with potassium hydroxide. A fixed-bed reactor is used for temperature swing adsorption of CO₂ in a gas mixture of N₂, O₂, and CO₂ to study the cyclic CO₂ adsorption capacity and selectivity of the produced activated carbons. The breakthrough adsorption capacity of the produced activated carbon is measured under a flue gas condition of 15 mol % of CO₂, 5 mol % of O₂, and 80% of N₂ at 25 °C and atmospheric pressure. Slow pyrolysis based activated carbon has a lower surface area and total pore volume but higher adsorption capacity in the presence of N₂. Sawdust based activated carbon synthesized using the slow pyrolysis process creates the highest ultra-micropore volume of 0.36 cm³/g, and the highest adsorption capacity in N₂ (78.1 mg/g) but low selectivity (2.8) over O₂ because of the oxygen functional groups on the surface. Ultra-micropores and surface chemistry of adsorbents are far more important than particle size, total pore volume, and internal surface area of the adsorbents. All the samples fully recovered their initial adsorption capacity in each cycle (for up to 10 cycles). This work also demonstrates that adsorption capacity and selectivity of activated carbon can be controlled and optimized through the choice of starting material and carbonization conditions

Environmental Occurrence and Toxicity of 6PPD Quinone, an Emerging Tire Rubber-Derived Chemical: A Review

N-(1,3-Dimethylbutyl)-N′-phenyl-p-phenylene­diamine (6PPD) is a chemical added to tires to prevent their oxidative degradation. 6PPD is highly reactive with ozone and oxygen, leading to the formation of transformation products such as 6PPD quinone (6PPDQ) on the tire surfaces and, subsequently, in tire and road wear particles. 6PPDQ is a toxicant that has been found in roadway runoff and receiving water systems. Its presence in municipal stormwater has led to the acute mortality of coho salmon during their migration to urban creeks to reproduce, generating global interest in studying its occurrence and toxicity in the environment. This review aims to provide a critical overview of the current state of knowledge of 6PPDQ, assisting researchers and policymakers in understanding the potential impacts of this emerging chemical on the environment and human health. As there are many unanswered questions surrounding 6PPDQ, further research is needed. This review highlights the importance of including transformation products in regulations for 6PPD, as well as all emerging synthetic chemicals of concern