Steam Reforming of Ethanol Using Ni–Co Catalysts Supported on MgAl₂O₄: Structural Study and Catalytic Properties at Different Temperatures

Abstract

A spectroscopic and microscopic investigation was made of the dynamics of bimetallic nanoparticles (NPs) in Co− Ni/MgAl 2 O 4 catalysts used for the steam reforming of ethanol (SRE) reaction, considering the implications for catalytic performance, shedding light on the elusive effect of Co−Ni alloy in reforming reactions. X-ray absorption spectroscopy (XAS) analyses showed that contact with the reagent mixture led to major changes in the superficial structure of the Co−Ni nanoparticles, which were strongly dependent on temperature and the metal particle size. At room temperature, contact between the Co−Ni NPs and the reactants (ethanol and H 2 O) led to the formation of a Co−Ni oxide film over the Co−Ni metal core, with CoO/NiO = 1. For smaller Co−Ni NPs (about 5 nm), the oxide film showed a dynamic composition according to temperature, with Co migrating to the surface while being oxidized up to around 350 °C. A structure with a core of (Co,Ni) and a shell rich in CoO was formed, which could be reduced above 350 °C. The surface CoO was mainly reduced upon heating in the reaction stream, with migration into the NP cores. For larger Co−Ni NPs (about 10 nm), the oxide film remained stable up to 200 °C, being reduced by the ethanol stream at higher temperatures. At operating temperatures in the range of 350−400 °C, the surface structure of the Ni−Co alloy showed (Ni,Co)−O species, while these metal oxide species decreased with increases of the thermal treatment temperature and the nanoparticle size. At low temperatures, the Co−Ni nanoparticles were covered by CoO/NiO and were active for the oxidative dehydrogenation of ethanol. With the increase of temperature, surface CoO was reduced and incorporated in the Co−Ni nanoparticle core. These metal sites became active toward the reactant and catalyzed the dehydrogenation of ethanol, followed by C−C bond cleavage, resulting in the formation of CH 4 , CO, and H 2 . The presence of CoO at the surface of the smaller Co−Ni nanoparticles suppressed carbon accumulation, compared to larger Co−Ni or Ni nanoparticles that had highly reduced surfaces.

Tuning CO2 Hydrogenation Selectivity by N-Doped Carbon Coating over Nickel Nanoparticles Supported on SiO2

“…2.9 Å can be assigned to Ni−Ni scattering paths of NiO, in agreement with the distances obtained for the reference bulk samples. 35,36 The scattering path at 2.04 Å correlates well with the Ni−O bond distance; however, it can also be attributed to Ni-light elements (C, N) at Ni5@NC/ SiO 2 . Bond lengths in the range of 1.9−2.1 Å were observed for Ni/N−C structures prepared from pyrolysis of the Ni(phen) 3 complex on MgO.…”

NaBH4-Assisted Synthesis of B–(Ni–Co)/MgAl2O4 Nanostructures for the Catalytic Dry Reforming of Methane

“…The SAED pattern displays the bright dots and dotted rings corresponding to metal and MA support, respectively (Figure S3c). Furthermore, the elemental mapping using HAADF S-TEM analysis for the catalyst is represented in Figure e. A uniform distribution of individual elements was observed for the B–(75Ni–25Co)/MA catalyst prepared by the one-step NaBH 4 reduction method.…”

“…The SAED pattern displays the bright dots and dotted rings corresponding to metal and MA support, respectively (Figure S3c). 47 Furthermore, the 5a. The H 2 desorption profile followed similar trends for all catalysts.…”

Activity Enhancement of PtIr Catalysts for Complete Ethanol Oxidation Reaction by Tuning C–O Coupling Abilities

“…42−44 Additionally, Rh, Ni, and Co were used for ethanol reforming. 45,46 Pt-based catalysts including Pt alloys represent the most commonly used and investigated anode materials for the EOR process. 20,41,47−51 However, Pt-based catalysts fail to achieve the desired EOR performance under operando conditions, resulting from the unavoidable CH 3 COOH formation and the poisoning of active sites caused by strongly adsorbed C 1 intermediates.…”

“…Therefore, a complete EOR comprises three overlapping stages of reactions: dehydrogenation of C 2 H x O species ( x = 1–6), C–C bond cleavage of C 2 H x O, and water dissociation and the conversion of C 1 intermediates into CO 2 . The most investigated critical factors in achieving a complete EOR are the reactions leading to the C–C bond cleavage and the acetic acid formation, while the most investigated catalysts consist of Pt , and Ir , followed by Pd and Cu. − Additionally, Rh, Ni, and Co were used for ethanol reforming. , …”