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

Abstract

As the search for carbon-efficient synthesis pathways for green alternatives to fossil fuels continues, an expanding class of catalysts have been developed for the upgrading of lower alcohols. Understanding of the acid base functionalities has greatly influenced the search for new materials, but the influence of the metal used in catalysts cannot be explained in a broader sense. We address this herein and correlate our findings with the most fundamental understanding of chemistry to date by applying it to d-band theory as part of an experimental investigation. The commercial catalysts of Pt, Rh, Ru, Cu, Pd, and Ir on carbon as a support have been characterized by means of SEM, EDX-mapping, STEM, XRD, N2-physisorption, and H2-chemisorption. Their catalytic activity has been established by means of c-methylation of ethanol with methanol. For all catalysts, the TOF with respect to i-butanol was examined. The Pt/C reached the highest TOF with a selectivity towards i-butanol of 89%. The trend for the TOFs could be well correlated with the d-band centers of the metal, which formed a volcano curve. Therefore, this study is another step towards the rationalization of catalyst design for the upgrading of alcohols into carbon-neutral fuels or chemical feedstock.

Dilute Alloy Catalysts for the Synthesis of Isobutanol via the Guerbet Route: A Comprehensive Study

“…The Cu 99 Fe 1 /C catalyst, now theoretically coinciding with an iridium d-band center, should, therefore, exhibit the same TOF, but remains behind the iridium with a maximum of 3.65/h. Iridium on a carbon support has a TOF of 9.58/h [12]. Similarly, the Ni 99 Pt 1 /C catalyst, with a d-band center of −2.09 eV, only reaches a maximum TOF value of 2.24/h, while it should have a value in the range of 10/h to 12/h.…”

“…The monometallic catalysts previously investigated in [12] exhibit a volcano plot and are depicted as stars. The TOF was calculated based on the atoms actually available for adsorption processes.…”

“…In our recent work, we demonstrated that the d-band model, developed by Hammer and Nørskov [11], provides a robust explanation for the reactivity trend of monometallic catalysts with d-metals [12]. Widely acknowledged in the scientific community, the d-band model correlates the d-band center with reactivity across various chemical reactions.…”

“…After impregnation, drying was carried out using a rotary evaporator at 40 mbar and a 40 • C water bath temperature for one hour at 6 rpm. Subsequently, it was calcined in portions of 1 g to 2 g in quartz glass crucibles in a tube furnace under a N 2 flow of 0.5 g/min at 500 • C for 4 h. The calcination was followed by a reduction of the catalysts in 2% H 2 in N 2 for 1 h at 250 • C. The catalysts obtained in this manner are listed in Table S3 and were tested and analyzed according to the procedure described in [12].…”

“…In this study, we aim to test bimetallic catalysts with predicted d-band centers in the range of −2.8 eV to −2 eV in the synthesis of isobutanol, since catalysts in this region showed high productivity in terms of TOF in our former experiments stated above [12]. Ruban et al calculated the d-band centers for the materials Cu 99 Ni 1 , Cu 99 Fe 1 , Ni 99 Pt 1 , Fe 99 Pd 1 , and Fe 99 Pt 1 in the range of −2.01 eV to −2.40 eV when the surface of the base metal (Cu, Ni, Fe) was doped with one percent of the dopant metal (Ni, Fe, Pt, or Pd).…”