Carbide Dihydrides: Carbonaceous Species Identified in Ta₄⁺‐Mediated Methane Dehydrogenation

Abstract

The products of methane dehydrogenation by gas‐phase Ta4+ clusters are structurally characterized using infrared multiple photon dissociation (IRMPD) spectroscopy in conjunction with quantum chemical calculations. The obtained spectra of [4Ta,C,2H]+ reveal a dominance of vibrational bands of a H2Ta4C+ carbide dihydride structure over those indicative for a HTa4CH+ carbyne hydride one, as is unambiguously verified by studies employing various methane isotopologues. Because methane dehydrogenation by metal cations M+ typically leads to the formation of either MCH2+ carbene or HMCH+ carbyne hydride structures, the observation of a H2MC+ carbide dihydride structure implies that it is imperative to consider this often‐neglected class of carbonaceous intermediates in the reaction of metals with hydrocarbons.

Room-Temperature Methane Activation Mediated by Free Tantalum Cluster Cations: Size-by-Size Reactivity

“…Similarly, it seems unlikely that the second dehydrogenation is too fast for the H/D-exchange reaction to compete with, when one considers that for products of Ta + and Ta 2 + this exchange is clearly visible in spite of much faster dehydrogenation reactions. Instead, this peculiar behavior may rather be related to the particular structure of [Ta 4 (CH 2 )] + , which was identified by us with IR spectroscopy of exhibiting a carbide dihydride structure, that is, H 2 Ta 4 C + …”

“…“H/D exchange” indicates whether this reaction was directly observed or required in the simulations (“yes) or it could have been omitted (“no”). “moieties bound to tantalum” gives the functional groups for C and H species from our calculations (see section to follow) or the literature (in case of [TaCH 2 ] + , and [Ta 4 (CH 2 )] + and [Ta 4 (CH 2 ) 2 ] + ). When the species represent the final product of the different reaction with methane, it is denoted by “product”. b Rate coefficients referenced to [TaCH 2 ] + formation determined by Shayesteh et al .…”

“…The theoretical explorations of the atomic arrangements and electronic structures of the bare tantalum clusters and their interactions and reactions with methane molecules were performed (as in our previous investigation , involving Ta) with the use of the Born–Oppenheimer (BO) spin density-functional theory (SDFT) molecular dynamics (BO-SDFT-MD) method with norm-conserving soft (scalar relativistic for Ta) pseudopotentials and the generalized gradient approximation (GGA) for electronic exchange and correlations (using the so-called PBE functional). A complete description of our computational methodology has been detailed in our earlier publication (see, e.g., ref ), and it is repeated here in its entirety in order to make this manuscript self-contained and for the sake of the readers’ convenience.…”

Conversion of CH4 Catalyzed by Gas Phase Ions Containing Metals

“…While gas phase ions containing noble metals have good activity toward coupling of CH 4 molecules, researchers have also paid attention to ions containing non‐noble metals to find active species exhibiting comparable performance with noble metal systems. The reactions of positively charged bare tantalum clusters Ta n + ( n =1‐10) and oxygen deficient Ta n O m + ( m =1 and 2) clusters with CH 4 have been systematically investigated by a cryogenic ring electrode ion trap [12k,35,45,52] . It was found that the Ta 8 O 2 + cluster has the ability to catalyze the C−C coupling of two CH 4 to generate C 2 H 6 [35] .…”

Ion spectroscopy in methane activation

“…The relative energies (in eV) of the corresponding structural isomers with respect to isomer II, the carbyne hydride. Adapted with permission from reference Lengyel et al (2020). Copyright (2020) Wiley‐VCH [Color figure can be viewed at wileyonlinelibrary.com]…”