Construction of Cu–Ce/graphene catalysts via a one-step hydrothermal method and their excellent CO catalytic oxidation performance

Effect of Modifying Carbon Materials with Metal Phthalocynines and Palladium on Their Catalytic Activity in ORR

Bimetallic catalysts based on multi-walled carbon nanotubes (MWCNT), graphene oxide (GO) and ultradispersed diamonds (UDD) supports for the process of electroreduction of oxygen from alkaline electrolyte were obtained using high-temperature synthesis. The materials were characterized by low-temperature nitrogen adsorption, Raman spectroscopy, scanning electron microscopy and X-ray structure analysis. The synthesized bimetallic catalysts contain meso- and micropores. Based on the study by Raman spectroscopy, it is shown that high-temperature synthesis of MWCNT with metal phthalocyanines leads to doping of this material with nitrogen and the appearance of significant defects in the structure. Carbon nanotube-based catalysts showed enhanced activity compared to other carbon materials. Moreover, bimetallic catalysts based on cobalt phthalocyanine and palladium (MWCNT_CoPc_Pd) are characterized by higher activity on all carbon supports compared to materials contain on copper and palladium. The specific current density in the diffusion region of the MWCNT_CoPc_Pd catalyst is comparable to a commercial platinum electrode (Pt(20%)/C) and equals to 2.65 mA/cm2. The area of the electrochemically active surface of all the obtained catalysts was calculated from the CV data in a nitrogen atmosphere. The MWCNT_CoPc_Pd catalyst is characterized by high corrosivity: after 2500 revolutions, the current density in the diffusion region decreases by 7%, and, also, an increase in the values of E1/2 and Eonset is observed.

The influence of support composition on the activity of Cu:Ce catalysts for selective catalytic reduction of NO by CO in the presence of excess oxygen

Excellent catalytic performance for NO reduction by CO in the presence of 5% O₂ over Cu1:Ce3/Al₂O₃.

Morphology effects on surface chemical properties and lattice defects of Cu/CeO2 catalysts applied for low-temperature CO oxidation

Here, we synthesized a series of Cu/CeO2 catalysts with different morphology and size, including Cu/CeO2 nanospheres (Cu/CeO2-S), Cu/CeO2 nanoparticles (Cu/CeO2-P), Cu/CeO2 nanorods (Cu/CeO2-R) and flower-like Cu/CeO2 microspheres (Cu/CeO2-F) to systematically explore the structure-activity relationship in CO oxidation. Crucially, the effect of morphology, crystal size, Ce4+/Ce3+ species, oxygen vacancies derived from the removal of lattice oxygen (Olatt) species in CeO2 and lattice defect sites on CO activity was revealed through various characterizations. It was clearly discovered that the activity of these catalysts was as follows: Cu/CeO2-R > Cu/CeO2-P > Cu/CeO2-S > Cu/CeO2-F, and the Cu/CeO2-R catalyst preferentially showed the best catalytic performance with a 90% conversion of CO even at 58 °C, owned the smaller particles size of CeO2 and CuO, and exhibited the higher concentration of Olatt species and oxygen vacancies. Besides, it is also verified that the Cu/CeO2-F sample exhibited the larger CeO2 crystal size (17.14 nm), which led to the lower Cu dispersion and CO conversion, even at 121 °C (T90). Most importantly, we discovered that the amount of surface lattice defect sites was positively related to the reaction rate of CO. Simultaneously, DFT calculation also demonstrated that the introduced oxygen vacancies in CeO2 could accelerate the oxidation of CO by the alteration of CO adsorption energy. Therefore, the morphology, the crystal size, the content of oxygen vacancies, as well as lattice defects of Cu/CeO2 catalyst might work together for CO oxidation reaction.