Activation of Methane on NiO Nanoparticles with Different Morphologies

Abstract

Superfícies nanoestruturadas podem ser definidas como substratos tendo como principal característica dimensões na faixa de 1-100 nm. O recente interesse nestes sistemas é baseado no fato de que novas e interessantes propriedade (catalíticas, magnéticas, ferroelétricas, mecânicas, óticas e eletrônicas) são desenvolvidas como resultado da redução da dimensão destes substratos. Neste trabalho descreve-se a decomposição catalítica do metano em hidrogênio e nanofilamentos de carbono em catalisadores não suportados de Ni preparados por metodologias distintas. Catalisador de Ni suportado em zircônia foi usado para comparação dos resultados. Para os catalisadores não suportados, observou-se forte dependência da atividade do catalisador com o tamanho da partícula do óxido precursor e sua morfologia. Apesar de todos terem apresentado dimensões na faixa de nanopartículas, somente os preparados usando etileno glicol, NiEG, e rota hidrotérmica, NiHT, exibiram a mesma performance que o catalisador suportado (atividade e estabilidade), 25NiZ. O catalisador sintetizado em presença de dimetilglioxima, NiDMG, foi o menos ativo e desativou com o tempo em operação. Nanostructured surfaces can be defined as substrates in which the typical features have dimensions in the range of 1-100 nm. The recent focus of interest in these systems is based on the fact that interesting novel properties (catalytic, magnetic, ferroelectric, mechanical, optical and electronic) are developed as a result of the dimension reductions of these substrates. This paper describes the catalytic methane decomposition into hydrogen and carbon nanofilaments on unsupported Ni catalysts prepared from different methodologies, with controlled particle size and morphologies. Ni catalyst supported on zirconia was also used for performance comparison. For the unsupported catalysts, it was observed strong dependency of catalyst activities with particle size of nickel oxide precursors and their morphologies. Although all of them presented crystallite sizes with nanometric dimensions, only those prepared with ethylene glycol, NiEG, and by hydrothermal condition, NiHT, exhibited the same performance as the supported catalyst (activity and stability), 25NiZ. Catalyst synthesized in the presence of dimethylglyoxime, NiDMG, was less active and deactivated with time on stream.

Influence of the Calcination Technique of Silica on the Properties and Performance of Ni/SiO2 Catalysts for Synthesis of Hydrogen via Methane Cracking Reaction

“…Figure 4b depicts the wide-angle XRD patterns of the Ni catalysts obtained by the reduction of NiO under hydrogen atmosphere at 700 °C, which found that all catalysts exhibited similar diffraction peaks at 2θ = 44.5, 51.8, and 76.4, corresponding to (111), (200), and (220) planes of metallic Ni with the absence of NiO peaks observed. 26 This suggests that during the reduction of the catalysts, Ni 2+ of NiO can be completely reduced to the active form of Ni 0 . 27 Besides, the Ni crystalline size, as listed in Table 1, can also be calculated by Scherrer's equation from the (111) plane.…”

Oscillatory Behaviour of Ni Supported on ZrO2 in the Catalytic Partial Oxidation of Methane as Determined by Activation Procedure

“…According to this pathway, we suggest that the active sites for the CH 4 -CPO on Ni/ZrO 2 catalysts should be poly-nuclear metal sites at the metal particle boundary, in a specific configuration. A similar proposal on the presence of cooperating nearby sites has been made to explain the catalytic activity of Ni supported on grafted ZrO 2 -Al 2 O 3 catalysts [ 36 ]. The amount of poly-nuclear metal active sites was lower in the Ni/Z ( red ) than in the Ni/Z ( ox-red ) catalysts because, in the Ni/Z ( red ), some Ni δ+ carbide-like species formed, inducing CPO oscillation.…”

“…In the literature, the CH 4 -CPO mechanism was described as a direct oxidation route, requiring several Ni sites able to activate methane and oxygen in adjacent positions (Ni–C, Ni–O and Ni–H) [ 14 , 17 , 36 , 60 ]. According to this pathway, we suggest that the active sites for the CH 4 -CPO on Ni/ZrO 2 catalysts should be poly-nuclear metal sites at the metal particle boundary, in a specific configuration.…”

“…Zirconium oxide is widely used as a support because of its high thermal stability and characteristic textural properties that can be tailored according to different preparation methods and thermal treatments, yielding the formation of monoclinic, metastable tetragonal or mixed tetragonal-monoclinic ZrO 2 phases [ 27 , 28 , 29 ]. Many papers have extensively investigated Ni-supported ZrO 2 systems for syngas production focussing on the support preparation methods and on the deposition of Ni precursors to obtain metal particle sizes suitable for high catalytic performances and low carbon deposition [ 11 , 14 , 30 , 31 , 32 , 33 , 34 , 35 , 36 ]. By contrast, the effect of ZrO 2 modifications on the metal dispersion and on the structure–activity relationship has not been clearly established thus far.…”