Contents lists available at ScienceDirect Catalysis Communications journal homepage: www.elsevier.com/locate/catcom Short communication N 2 O-assisted methanol selective oxidation to formaldehyde on cobalt oxide catalysts derived from layered double hydroxides Oséas S. Santos a , Artur J.S. Mascarenhas a,b , Heloysa M.C. Andrade a,b, ⁎ a Laboratório de Catálise e Materiais, Departamento de Química Geral e Inorgânica, Instituto de Química, Universidade Federal da Bahia, Trav. Barão de Jeremoabo, 147, Campus de Ondina, 40170-280 Salvador, BA, Brazil b Instituto Nacional de Ciência e Tecnologia em Energia e Ambiente (INCT – E&A), Centro Interdisciplinar de Energia e Ambiente (CIENAM), Campus de Ondina, 40170- 115 Salvador, BA, Brazil ARTICLE INFO Keywords: Nitrous oxide (N 2 O) Selective oxidation of methanol Formaldehyde Layered double hydroxides (LDH) ABSTRACT Cobalt-magnesium-aluminum oxides derived from layered double hydroxides were used as catalysts for the conversion of methanol to formaldehyde in the presence of nitrous oxide. The catalysts were characterized by XRD, FTIR, UV–vis DRS, TPR-H 2 , NH 3 - and CO 2 -TPD and N 2 adsorption. 100% methanol conversion and 91% selectivity to formaldehyde were simultaneously obtained with 100% N 2 O conversion at 440 °C over a Co,Mg,Al- mixed oxide catalyst. Higher hydrogen yields and lower CO and CO 2 yields were obtained than when air was used as oxidizing agent, under the same conditions. These findings suggest that the reaction occurs on a com- bination of redox and basic catalytic sites. 1. Introduction Nitrous oxide (N 2 O) is an environmental pollutant that contributes to the greenhouse effect and destruction of ozone in the stratosphere. Due to the high thermal decomposition temperature of N 2 O, which occurs above 600 °C [1,2], the use of efficient catalysts is necessary to conduct this reaction, thus ensuring the minimization of atmospheric emissions from anthropogenic sources, such as nitric acid and adipic acid industrial plants. Alternatively, the use of N 2 O as oxidant agent for hydrocarbon conversion to useful products is an interesting strategy to mitigate these emissions and develop new technologies [3–5]. About 32% of the methanol produced worldwide is consumed in the production of formaldehyde [6], therefore the use of N 2 O as oxidant agent to selectively produce formaldehyde is of great technological and environmental interest. Two main classes of catalysts are employed in the partial oxidation of methanol to formaldehyde: (i) silver catalysts, operating in the temperature range of 580–650 °C; or (ii) iron-molybdenum catalysts operating in the temperature range of 400 °C [7–10]. Based on a DFT study, M.F. Fellah [11] showed that the direct oxidation of methanol to formaldehyde using N 2 O would be possible on [Fe-O] + species in Fe- ZSM-5. Khan et al. [4] reported on the use of Co-ZSM-5 catalysts to partially oxidize methane to synthesis gas using N 2 O as oxidant. In early papers, Co-ZSM-5 and Co-oxides derived from hydrotalcites (LDH) were reported as efficient catalysts for decomposition of N 2 O[12,13]. Gen- nequin et al. [14] used Co,Mg,Al-hydrotalcites as catalyst precursors for the total oxidation of volatile organic compounds and showed that the high activity for toluene oxidation of the Co-rich catalysts was related to the presence of easily reducible Co 3 O 4 particles. Thus, considering that cobalt catalysts are active both for N 2 O de- composition and for oxidation reactions, the selective conversion of methanol to formaldehyde was investigated using N 2 O as oxidant and Co-oxides derived from hydrotalcites as catalysts in the present study. 2. Experimental 2.1. Catalysts preparation MgAl (1:1), CoAl (1:1), CoMgAl (1:2:1) and CoMgAl (2:1:1) LDH samples were prepared by coprecipitation, using solutions of the metal nitrates and Na 2 CO 3 /NaOH solution, at pH = 11 [14]. The gels were aged at 80 °C for 24 h, then filtered and washed with distilled water until the pH was 10. The LDH samples were calcined at 600 °C in air for 4 h before reaction, obtaining the mixed oxide, respectively named as MgAl, CoAl, CoMgAl-1 and CoMgAl-2. https://doi.org/10.1016/j.catcom.2018.05.014 Received 7 April 2018; Received in revised form 21 May 2018; Accepted 22 May 2018 ⁎ Corresponding author at: Laboratório de Catálise e Materiais, Departamento de Química Geral e Inorgânica, Instituto de Química, Universidade Federal da Bahia, Trav. Barão de Jeremoabo, 147, Campus de Ondina, 40170-280 Salvador, BA, Brazil. E-mail address: handrade@ufba.br (H.M.C. Andrade). Catalysis Communications 113 (2018) 32–35 Available online 23 May 2018 1566-7367/ © 2018 Elsevier B.V. All rights reserved. T