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Future emission standards are becoming increasingly stringent. Around 50% of targeted tailpipe emissions are emitted during the cold-start period, mainly due to the ineffectiveness of catalytic converters in the after-treatment system at low temperatures (<200 °C). Passive NOxadsorbers (PNA) have been proposed to help address cold start NOxemissions problems. Among various PNAs, the distinctive properties of Pd/zeolites match perfectly with the required characteristics of PNA catalysts for vehicle emission control. This review summarizes significant advances in Pd/zeolite applied to PNAs, including NO storage sites, NOxadsorption and release chemistry, synthesis methodology, and deactivation mechanisms. Future outlooks and challenges ahead for Pd/zeolite catalyst development and fundamental research are also proposed. Collectively, this review provides a theoretical and experimental foundation for the rational fabrication and application of PNA catalysts toward NOxemission control.

Ce and La doped Co3O4nanorod catalysts were prepared and their catalytic activity for CO and C3H6oxidation reactions was examined. XRD, TEM, XPS, TPR, TGA and in situDRIFTS have been used to characterize structural properties, reducibility, mobility of adsorbed oxygen and lattice oxygen, and surface intermediates for both CO and C3H6oxidation. When doping with either Ce or La, the cations occupy the Co2+sites in Co3O4. XPS, TPR, and TGA characterization showed that the Ce dopant decreased the ratio of surface adsorbed oxygen to lattice oxygen, and facilitated the extraction of adsorbed oxygen and lattice oxygen with hydrogen from CeO2–Co3O4in comparison to Co3O4, while the La dopant caused the opposite effect. The light-off performance for both CO and C3H6oxidations has been improved due to Ce doping on Co3O4, while the doping of La actually inhibited the oxidation activity of the Co3O4catalyst. Similar catalytic activity facilitation and inhibition of Ce and La dopants were also observed for the simultaneous oxidation of CO, C3H6, and NO under the conditions of simulated diesel exhaust. The results of in situDRIFTS suggested that bidentate carbonate species could be the key intermediates of CO oxidation, which would further react with CO to form CO2. The results of DRIFTS showed that the mobility of lattice oxygen plays an important role in the C3H6oxidation. A mechanism was proposed where the formate and acetate species could be the reaction intermediates of C3H6oxidation, and these intermediates are more stable on La2O3–Co3O4than on Co3O4and CeO2–Co3O4catalysts.

In the present study, removal of Pb(II) ions using γ-Alumina was investigated. γ-Alumina used in the present study was prepared by gel combustion method. The XRD revealed that the synthesized particle was in amorphous phase and the SEM image showed highly porous surface which is a characteristic property of a good adsorbent. The pore size and surface area of the γ-Alumina were determined and found to be 243m2/g and 41Å, respectively. The effects of pH, initial lead concentration, adsorbent dosage on the extent of adsorption and time of contact were studied. Atomic absorption spectrometer (AAS) was used to determine the concentration of lead after adsorption. The Pb(II) removal capacity of γ-Alumina was found to be maximum at pH 7. From the Langmuir isotherm the maximum adsorption capacity of γ-Alumina toward Pb(II) was determined (Q0=65.67mg/g). Compared to other metal oxides γ-Alumina showed a significantly higher adsorption capacity. Although Pb(II) adsorption occurred in the first 35min of contact time, at least 90min to attain equilibrium. The kinetics of adsorption can be described by first order rate equation. Statistically based experimental model such as Box–Behnken Method (BBM) was used to study the effect of variables on adsorption. Regeneration studies of the adsorbent were carried out and it was found that the adsorbent can be effectively regenerated upto 3 times with significant level of adsorption. The results suggest that γ-Alumina is effective adsorbent for the removal of lead.