A Study of Different Doped Metal Cations on the Physicochemical Properties and Catalytic Activities of Ce₂₀M₁O_x (M=Zr, Cr, Mn, Fe, Co, Sn) Composite Oxides for Nitric Oxide Reduction by Carbon Monoxide

Abstract

This work is mainly focused on investigating the effects of different doped metal cations on the formation of Ce20 M1 Ox (M=Zr, Cr, Mn, Fe, Co, Sn) composite oxides and their physicochemical and catalytic properties for NO reduction by CO as a model reaction. The obtained samples were characterized by using N2 physisorption, X-ray diffraction, laser Raman spectroscopy, UV/Vis diffuse reflectance spectroscopy, inductively coupled plasma atomic emission spectroscopy, X-ray photoelectron spectroscopy, temperature-programmed reduction by hydrogen and by oxygen (H2 -TPR and O2 -TPD), in situ diffuse reflectance infrared Fourier transform spectroscopy, and the NO+CO model reaction. The results imply that the introduction of M(x+) into the lattice of CeO2 increases the specific surface area and pore volume, especially for variable valence metal cations, and enhances the catalytic performance to a great extent. In this regard, increases in the oxygen vacancies, reduction properties, and chemisorbed O2 (-) (and/or O(-) ) species of these Ce20 M1 Ox composite oxides (M refers to variable valence metals) play significant roles in this reaction. Among the samples, Ce20 Cr1 Ox exhibited the best catalytic performance, mainly because it has the best reducibility and more chemisorbed oxygen, and significant reasons for these attributes may be closely related to favorable synergistic interactions of the vacancies and near-surface Ce(3+) and Cr(3+) . Finally, a possible reaction mechanism was tentatively proposed to understand the reactions.

Novel multi-drug delivery hydrogel using scar-homing liposomes improves spinal cord injury repair

“…Another major factor in the efficacy of CAQK-LIP-GFs/DTX@HP in treating SCI is the neuroprotection of GFs, including their local immune-modulatory action and effects in promoting neuronal plasticity 46 . It is widely acknowledged that a pronounced microglia/macrophage response is induced after SCI via the release of pro-inflammatory cytokines, nitric oxide (NO), and reactive oxygen species (ROS) by M1 macrophages 69 , 70 , which leads to ECM degradation, scar formation, neuron death and axon retraction 71 , 72 . Our data suggest that GFs likely promote tissue repair and ECM remodeling in part by inhibiting the spread of M1 macrophages and increasing the activation and/or proliferation of M2 macrophages during the early post-lesion phase.…”

Ceria-Based Catalysts Studied by Near Ambient Pressure X-ray Photoelectron Spectroscopy: A Review

“…A well-known method to notably enhance cerium oxide redox activity is the addition of 3d transition metals to its unit cell to form solid solutions with an ordered atomic arrangement [3,102]. For instance, it has been demonstrated that Ce 1−x M x O 2−y mixed oxides (where M = Cr [103,104], Mn [104][105][106], Fe [104,106], Co [104][105][106], Ni [105,106], Cu [107,108], Zr [109][110][111], La [112][113][114]) exhibit lower reduction temperatures than pure ceria. The incorporation of noble metals to ceria to generate Ce 1−x M' x O 2−y mixed oxides (M' = Ru [115], Rh [116,117], Pd [117,118]) has also demonstrated to efficiently promote reducibility of cerium ions and greatly decrease the reduction temperatures too [119].…”

Synergistic Effect of Simultaneous Doping of Ceria Nanorods with Cu and Cr on CO Oxidation and NO Reduction

“…Various other ceria catalysts doped with copper or chromium have recently been reported [14, 21, 22, 61, 62] . Direct comparisons with other articles is difficult due to differences in reaction conditions such as catalyst loading and reactant flowrates or ratios, which widely vary between different research groups.…”

“…In contrast, for NO reduction, our Cu/Cr‐doped ceria nanorods performed slightly better at 150 °C but somewhat worse at 200 °C compared with a Cr‐doped ceria catalyst (Ce 20 Cr 1 O x ) or a 0.07 % each Cu/Cr deposited on ceria (Table 2). [22] In any case, the latter uses a pulsed cathodic arc plasma technique in vacuum, much more complicated than our hydrothermal approach.…”

“…[18] While the suitability of doped ceria for CO oxidation has been widely examined, investigationi nto NO x reduction has been less exhaustive. [19][20][21][22][23][24][25][26][27] While doping of ceria is generally a good strategyf or catalytic oxidation reactions because it improvesr educibility and oxygen vacancy formation,t his can lead to at rade-off of reducing the favorability of oxygen vacancy healing, necessary to complete the catalytic cycle for NO x reduction. [28,29] For this reason,b oth reactions must be examined simultaneously.…”