Effect of preparation method on the solid state properties and the deN₂O performance of CuO–CeO₂oxides

Abstract

The present work aims at investigating the catalytic decomposition of N 2 O over CuO-CeO 2 single or mixed oxides prepared by different synthesis routes, i.e., impregnation, precipitation and exotemplating. To gain insight into the particular role of CeO 2 as well as of CuO-CeO 2 interactions, three different types of materials are prepared and tested for N 2 O decomposition both in the absence and presence of excess O 2 : (i) bare CeO 2 prepared by precipitation and exotemplating, (ii) CuO/CeO 2 oxides synthesized by impregnation of CeO 2 samples prepared in (i) with CuO and iii) single stage synthesized CuO-CeO 2 mixed oxides employing the coprecipitation and exotemplating methods. The corresponding commercial samples were also examined for comparison purposes. All materials were characterized by N 2 adsorption at -196 °C, X-ray diffraction (XRD), H 2 temperature-programmed reduction (H 2 -TPR), X-ray photoelectron spectroscopy (XPS), micro-Raman spectroscopy (micro-Raman) and scanning electron microscopy (SEM). The results demonstrated the key role of preparation procedure on the direct catalytic decomposition of N 2 O. Among the bare CeO 2 samples, the best performance was obtained with the samples prepared by the precipitation method, followed by exotemplating, while commercial CeO 2 showed the lowest performance. All bare oxides demonstrated low N 2 O conversion, never exceeding 40% at 600 °C. Amongst the CuO-CeO 2 oxides, the optimum performance was observed for those prepared by co-precipitation, which achieved complete N 2 O conversion at 550 ºC. In the presence of excess oxygen in the feed stream, a slight degradation is observed, with the sequence of deN 2 O performance to remain unchanged. The superiority of Cu-Ce mixed oxides prepared by precipitation compared to all other materials can be mainly ascribed to their excellent redox properties, linked to Ce 4+ /Ce 3+ and Cu 2+ /Cu + redox pairs. A redox mechanism for N 2 O catalytic decomposition is proposed involving N 2 O adsorption on Cu + sites and their regeneration through Cu-ceria interactions. and mobile emissions is nowadays a challenging environmental issue.Several after-treatment techniques have been developed for N 2 O abatement, including thermal decomposition 6 , non-selective catalytic reduction 4 , selective catalytic reduction 7,8 and direct catalytic decomposition 9-12 . Among these, direct catalytic decomposition of N 2 O (deN 2 O) is the most promising method, due to its high efficiency and low energy requirements. The decomposition of N 2 O has been studied on various catalytic systems, such as transition and noble metal catalysts, perovskites, hexaluminates, spinels, zeolites, etc 4,9,[13][14][15][16][17][18][19][20] . In spite of the excellent catalytic performance of noble metals (NMs)-based catalysts, their high cost and sensitivity to oxygen poisoning limit their practical applications 9 . Therefore, the development of NMs-free catalysts of low cost and adequate de-N 2 O performance is of crucial importance from both practical ...

Catalytic Behaviour of CuO-CeO2 Systems Prepared by Different Synthetic Methodologies in the CO-PROX Reaction under CO2-H2O Feed Stream

“…In all cases, the main contributions have been ascribed to the presence of Ce 4+ species, although Ce 3+ species have been also detected, as the Ce 3+ /Ce 4+ ratio indicates (Table 3). These data can be related to the H 2 -consumed/H 2 -theoretical ratio (Table 2) due to the formation of smaller particles that lead to a higher proportion of surface area, which is more easily reducible [61]. However, these data are not in accordance with the Raman spectra, so it is expected that Ce species tend to undergo a photoreduction process despite the short irradiation time.…”

Photo-reduced Cu/CuO nanoclusters on TiO2 nanotube arrays as highly efficient and reusable catalyst

“…Major peaks of Cu 2p 3/2 at 932.5 eV and Cu 2p 1/2 at 952.3 eV confirmed the existed of metallic copper202136, demonstrated the successful photoreduction of CuCl 2 . Meanwhile, the peaks of Cu 2p 3/2 at 934.6 eV and Cu 2p 1/2 at 954.6 eV in combination with the satellite peaks at 941.5 eV and 944.3 eV are typical characteristics of CuO203637, implying the uniformly surface oxidation of Cu nanoclusters exposed in air under ambient conditions. These results are consistent with the TEM characterization.…”

Synthesis and application of rare-earth elements (Gd, Sm, and Nd) doped ceria-based solid solutions for methyl mercaptan catalytic decomposition

“…The calculated results are listed in Table 1 species in pure CeO 2 mainly points out that the sample has not been fully oxidized, rather than represents for the formation of oxygen vacancies [22]). This phenomenon could be ascribed to the synergistic interaction between Gd and Ce oxides (as mentioned in the section of XRD characterization), which leads to the facilitation of redox cycles between Ce 3+ and Ce 4+ [32]. The O1s XP core level spectra of the RE doped and pure ceria catalysts are demonstrated in Fig.…”

“…More importantly, it is reported that the existence of Ce 3+ in doped ceria based catalysts is generally associated with the formation of oxygen vacancies, and higher concentration of Ce 3+ implies larger amounts of oxygen vacancies [31]. The relative Ce 3+ concentration can be determined by the ratio: Ce 3+ /(Ce 4+ + Ce 3+ ), where Ce 4+ and Ce 3+ represent the sums of the spectral peak areas related to the Ce 4+ and Ce 3+ , respectively [32]. The calculated results are listed in Table 1 species in pure CeO 2 mainly points out that the sample has not been fully oxidized, rather than represents for the formation of oxygen vacancies [22]).…”