Investigation of catalysts M/CeO2 (M = Pt, Rh, or Pd) for purification of CO2 derived from oxycombustion in the absence or presence of water.

Oxyfuel combustion is a promising technology to produce a CO2-rich flue gas ready suitable for sequestration or valorization. But its storage as well as its further valorization requires to increase the CO2 purification as a small amount of CO and NOx are produced during combustion. Based on the technology developed for three-way converters, similar systems, i.e., M/CeO2 where M is Pt, Pd, or Rh, were studied for NO-CO abatement in a gas stream similar to those obtained when an oxyfuel combustion is performed. The results evidenced that the role of the metal nature influences the performances obtained on NO-CO abatement, platinum supported on ceria being the most efficient catalyst. We also measured the impact of the presence of water in the reaction stream on the catalytic activity of these materials. It appears that the presence of water has a beneficial effect on the different reactions due to a water gas shift reaction that increases the reduction of the NO and favors the formation of N2. The study pointed out that platinum supported on ceria remained the best catalyst, under these wet operating conditions close to industrial ones, for purification of oxyfuel combustion exhausts.

Catalytic wet air oxidation of high BPA concentration over iron-based catalyst supported on orthophosphate.

The catalytic performance of Fe supported on nickel phosphate (NiP) was evaluated for the removal of bisphenol A (BPA) by catalytic wet air oxidation (CWAO) at 140 °C and 25 bar of pure oxygen pressure. The prepared NiP and Fe/NiP materials were fully characterized by XRD, N2-physisorption, H2-TPR, TEM, and ICP analysis. Iron (Fe/NiP) impregnation of NiP support enhanced the BPA removal efficiency from 37.0 to 99.6% when CWAO was performed. This catalyst was highly stable given the operating conditions of acidic medium, high temperature, and high pressure. The Fe/NiP catalyst showed an outstanding catalytic activity for oxidation of BPA, achieving almost complete removal of BPA in 180 min at a concentration of 300 mg/L, using 4 g/L of Fe/NiP. No iron leaching was detected after the CWAO of BPA. The stability of Fe/NiP was performed over three consecutive cycles, noting that BPA conversion was not affected and iron leaching was negligible. Therefore, this catalyst (Fe/NiP) could be considered as an innocuous and effective long-lasting catalyst for the oxidation of harmful organic molecules.

Porous carbon materials derived from olive kernels: application in adsorption of organic pollutants.

Adsorption of organic pollutants (OPs), bisphenol A, and diuron, from aqueous solutions onto porous carbon materials (CMs) prepared from olive kernels, have been investigated. The effects of initial pH, initial OP concentration, temperature, and contact time on the adsorption capacity were studied. The adsorption of bisphenol A and diuron onto CMs was found to be optimal at pH 5.6 and 6.9, respectively. It was noticed that the adsorption of those organic pollutants from aqueous solution declined with increasing temperature and the process is exothermic. The rate of adsorption followed the second order kinetic equation. The equilibrium results showed that Langmuir model fits well with the data. The maximum adsorption capacities obtained using the best CM were 476 and 434 mg g-1 for BPA and diuron, respectively. The results showed that CMs made from olive kernels are an excellent and inexpensive biomass waste-derived sorbent. Graphical abstract.

Preparation of mesoporous activated carbon from date stones for the adsorption of Bemacid Red.

This work concerns the elimination of the organic pollutant; Bemacid Red (BR), a rather persistent dye present in wastewater from the textile industry in western Algeria, by adsorption on carbon from an agricultural waste in the optimal conditions of the adsorption process. An active carbon was synthesized by treating an agro-alimentary waste, the date stones that are very abundant in Algeria, physically and chemically. Sample after activation (SAA) with phosphoric acid was highly efficient for the removal of BR. The characterization of this porous material has shown a specific surface area that exceeds 900 m2/g with the presence of mesopores. The iodine value also indicates that the activated carbon obtained has a large micro porosity. The reduction of the infrared spectroscopy (FTIR) bands reveals that the waste has been synthesized and activated in good conditions. Parameters influencing the adsorption process have been studied and optimized, such as contact time, adsorbent mass, solution pH, initial dye concentration and temperature. The results show that for a contact time of 60 min, a mass of 0.5 g and at room temperature, the adsorption rate of the BR by the SAA is at its maximum. Pseudo-first-order, pseudo-second-order and intraparticle diffusion models were studied to analyse adsorption kinetics. The result shows the adsorption kinetic is best with the pseudo-second-order model. In this study, Langmuir, Freundlich and Temkin isotherms were investigated for adsorption of BR onto SAA. The Freundlich and Temkin isotherms have the highest correlations coefficients. The suggested adsorption process involves multilayer adsorption with the creation of chemical bonds. The mechanism of adsorption of BR by SAA is spontaneous and exothermic, and the Gibbs free energy values confirm that the elimination of the textile dye follows a physisorption.

Catalytic degradation of O-cresol using H2 O2 onto Algerian Clay-Na.

Clay material is used as a catalyst to degrade an organic pollutant. This study focused on the O-cresol oxidative degradation in aqueous solution by adding H2 O2 and Mont-Na. The catalytic tests showed a high catalytic activity of Mont-Na, which made it possible to achieve more than 84.6% conversion after 90 min of reaction time at 55°C in 23.2 mM H2 O2 . The pH value was found to be negatively correlated with the degradation rate of O-cresol. UV-Vis spectrophotometry revealed that the increase of degradation rate at low pH is related to the formation of 2-methylbenzoquinone as intermediate product. In addition, the content of iron in Mont-Na decreased after the catalytic test, bringing further evidence about the O-cresol catalytic oxidation. The mineralization of O-cresol is also confirmed by the different methods of characterization of Mont-Na after the catalytic oxidation test. The effect of the O-cresol oxidation catalyzed by natural clay is significant. PRACTITIONER POINTS: Algerian Montmorillonite-Na is used as a catalyst to degrade an organic pollutant: O-cresol. It shows a great potential for catalyst properties in the presence of the oxidizing reagent H2 O2 . It proved to be an effective means for the degradation of O-cresol contained in wastewaters.

Palladium, Iridium, and Rhodium Supported Catalysts: Predictive H2 Chemisorption by Statistical Cuboctahedron Clusters Model.

Chemisorption of hydrogen on metallic particles is often used to estimate the metal dispersion (D), the metal particle size (d), and the metallic specific surface area (SM), currently assuming a stoichiometry of one hydrogen atom H adsorbed per surface metal atom M. This assumption leads to a large error when estimating D, d, and SM, and a rigorous method is needed to tackle this problem. A model describing the statistics of the metal surface atom and site distribution on perfect cuboctahedron clusters, already developed for Pt, is applied to Pd, Ir, and Rh, using the density functional theory (DFT) calculation of the literature to determine the most favorable adsorption sites for each metal. The model predicts the H/M values for each metal, in the range 0⁻1.08 for Pd, 0⁻2.77 for Ir, and 0⁻2.31 for Rh, depending on the particle size, clearly showing that the hypothesis of H/M = 1 is not always confirmed. A set of equations is then given for precisely calculating D, d, and SM for each metal directly from the H chemisorption results determined experimentally, without any assumption about the H/M stoichiometry. This methodology provides a powerful tool for accurate determination of metal dispersion, metal particle size, and metallic specific surface area from chemisorption experiments.