Ethanol Dehydrogenation: A Reaction Path Study by Means of Temporal Analysis of Products

Abstract

Conventional fossil fuels such as gasoline or diesel should be substituted in the future by environmentally-friendly alternatives in order to reduce emissions in the transport sector and thus mitigate global warming. In this regard, iso-butanol is very promising as its chemical and physical properties are very similar to those of gasoline. Therefore, ongoing research deals with the development of catalytically-supported synthesis routes to iso-butanol, starting from renewably-generated methanol. This research has already revealed that the dehydrogenation of ethanol plays an important role in the reaction sequence from methanol to iso-butanol. To improve the fundamental understanding of the ethanol dehydrogenation step, the Temporal Analysis of Products (TAP) methodology was applied to illuminate that the catalysts used, Pt/C, Ir/C and Cu/C, are very active in ethanol adsorption. H2 and acetaldehyde are formed on the catalyst surfaces, with the latter quickly decomposing into CO and CH4 under the given reaction conditions. Based on the TAP results, this paper proposes a reaction scheme for ethanol dehydrogenation and acetaldehyde decomposition on the respective catalysts. The samples are characterized by means of N2 sorption and Scanning Transmission Electron Microscopy (STEM).

Elucidating the Influence of the d-Band Center on the Synthesis of Isobutanol

“…The calculations established a mean particle diameter of 17 nm. These results deviate heavily from the TEM measurements, whereas they correspond to previously published TEM results [32]. The deviation can be explained by taking into account the local formation of large Cu-rich agglomerates.…”

“…-01:00 00:00 01:00 02:00 03:00 04:00 05:00 For Pt/C, we were able to prove a deposition of carbonaceous matter on the catalyst by pulsing the catalyst with ethanol under ultra-high vacuum (UHV) conditions, as recently published [32]. Taking into account the pressure gap, we anticipate coking processes to have been a reason for the catalyst deactivation.…”

“…As explained in the introduction, the d-band center correlates with the bond strength to a surface adsorbate [18]. In the i-butanol synthesis, different intermediates are produced, by bond cleavage (O-H, H-H, C-H) and formation of new bonds (C-C, C-H, O-H) [24,32]. Every intermediate possesses different molecular orbital energies.…”

“…Catalysts 2021, 11, x FOR PEER REVIEW 14 of 19 [24,32]. Every intermediate possesses different molecular orbital energies.…”

Ethanol Decomposition and Dehydrogenation for Hydrogen Production: A Review of Heterogeneous Catalysts

“…43 Figure 1 shows the possible surface intermediates based on the specific bond cleavage leading to the formation of byproducts such as acetaldehyde, ethylene, methane, and carbon monoxide, along with hydrogen. Formation of the ethoxy species are the commonly reported starting point in ED 16,44−46 on transition metals including Cu, Ni, Fe, and Co. 16,44,45,47,48 Pasel et al confirmed the formation of ethoxy species on Cu/C, Pt/C, and Ir/C catalysts using temporal analysis of products, and concluded that the ethoxy species further convert to shortlived surface aldehyde that can decompose generating other products. 48 The final stable product to be released from the reactor depends on the specific active sites, where acetaldehyde is observed as a stable product on copper, 16,24,45,49−51 methane and carbon monoxide on nickel, 16,45 higher hydrocarbons and carbon dioxide on iron, 16 and methane, carbon dioxide, acetate, and water on cobalt catalysts.…”