Cu-exchanged small-pore zeolites (CHA and AEI) form methanol from methane (>95% selectivity) using a 3-step cyclic procedure (Chem. Commun.20155144474450) with methanol amounts higher than Cu-ZSM-5 and Cu-mordenite on a per gram and per Cu basis. Here, the Cu x O y species formed on Cu-SSZ-13 and Cu-SSZ-39 following O2 or He activation at 450 °C are identified as trans-μ-1,2-peroxo dicopper­(II) ([Cu2O2]2+) and mono-(μ-oxo) dicopper­(II) ([Cu2O]2+) using synchrotron X-ray diffraction, in situ UV–vis, and Raman spectroscopy and theory. [Cu2O2]2+ and [Cu2O]2+ formed on Cu-SSZ-13 showed ligand-to-metal charge transfer (LMCT) energies between 22,200 and 35,000 cm–1, Cu–O vibrations at 360, 510, 580, and 617 cm–1 and an O–O vibration at 837 cm–1. The vibrations at 360, 510, 580, and 837 cm–1 are assigned to the trans-μ-1,2-peroxo dicopper­(II) species, whereas the Cu–O vibration at 617 cm–1 (Δ18O = 24 cm–1) is assigned to a stretching vibration of a thermodynamically favored mono-(μ-oxo) dicopper­(II) with a Cu–O–Cu angle of 95°. On the basis of the intensity loss of the broad LMCT band between 22,200 and 35,000 cm–1 and Raman intensity loss at 571 cm–1 upon reaction, both the trans-μ-1,2-peroxo dicopper­(II) and mono-(μ-oxo) dicopper­(II) species are suggested to take part in methane activation at 200 °C with the trans-μ-1,2-peroxo dicopper­(II) core playing a dominant role. A relationship between the [Cu2O y ]2+ concentration and Cu­(II) at the eight-membered ring is observed and related to the concentration of [CuOH]+ suggested as an intermediate in [Cu2O y ]2+ formation.

This communication reports the discovery of several small-pore Cu-zeolites and zeotypes that produce methanol from methane and water vapor, and produce more methanol per copper atom than Cu-ZSM-5 and Cu-mordenite. The new materials include Cu-SSZ-13, Cu-SSZ-16, Cu-SSZ-39, and Cu-SAPO-34.

The “hydrocarbon pool” mechanism for the conversion of methanol to hydrocarbons on H-form zeolites was first introduced more than two decades ago, but the details continue to be a topic of debate. In this contribution, the hydrocarbon pool on zeolites H-ZSM-5 and H-beta was investigated by applying in situ ultraviolet–visible (UV–vis) spectroscopy. The intensity of absorption bands that grew during an induction period were compared with formation rates of gas-phase products. Spectra of both catalysts revealed the presence of alkylbenzenium and alkyl-substituted cyclopentadienium ions; on H-beta, larger polycyclic aromatic compounds were also formed. An absorption band at 295 nm of species on H-ZSM-5, assigned to an alkyl-substituted cyclopentadienium ion with four or five alkyl groups, paralleled the increase in ethene formation rates during an induction period, thus implicating the participation of such cations in the rate-limiting step. The alkylbenzenium ions on H-ZSM-5 were characterized by an average of three to four alkyl groups, whereas the alkylbenzene compounds formed on H-beta were fully alkylated already after 7 min on stream. In both cases, the concentration of alkylbenzenium ions increased almost linearly with time and was not correlated with rates of formation of gas-phase products. Adsorption experiments with hexamethylbenzene and 1,2,3,4,5-pentamethylcyclopentadiene were used to provide a reference for detailed interpretation of UV–vis spectra. Spectra of the latter are the first reported of an alkyl-substituted cyclopentadienium cation on a zeolite.

Fe–K/Al2O3 is shown to be an effective RWGS catalyst with high CO selectivity.