Humanity already possesses the fundamental scientific, technical, and industrial know-how to solve the carbon and climate problem for the next half-century. A portfolio of technologies now exists to meet the world's energy needs over the next 50 years and limit atmospheric CO2 to a trajectory that avoids a doubling of the preindustrial concentration. Every element in this portfolio has passed beyond the laboratory bench and demonstration project; many are already implemented somewhere at full industrial scale. Although no element is a credible candidate for doing the entire job (or even half the job) by itself, the portfolio as a whole is large enough that not every element has to be used.

“Stabilization wedges: Solving the climate problem for the next 50 years with current technologies” from science magazine (2004)

The reactive oxidizing species in the selective oxidation of methane to methanol in oxygen activated Cu-ZSM-5 was recently defined to be a bent mono(μ-oxo)dicopper(II) species, [Cu(2)O](2+). In this communication we report the formation of an O(2)-precursor of this reactive site with an associated absorption band at 29,000 cm(-1). Laser excitation into this absorption feature yields a resonance Raman (rR) spectrum characterized by (18)O(2) isotope sensitive and insensitive vibrations, νO-O and νCu-Cu, at 736 (Δ(18)O(2) = 41 cm(-1)) and 269 cm(-1), respectively. These define the precursor to be a μ-(η(2):η(2)) peroxo dicopper(II) species, [Cu(2)(O(2))](2+). rR experiments in combination with UV-vis absorption data show that this [Cu(2)(O(2))](2+) species transforms directly into the [Cu(2)O](2+) reactive site. Spectator Cu(+) sites in the zeolite ion-exchange sites provide the two electrons required to break the peroxo bond in the precursor. O(2)-TPD experiments with (18)O(2) show the incorporation of the second (18)O atom into the zeolite lattice in the transformation of [Cu(2)(O(2))](2+) into [Cu(2)O](2+). This study defines the mechanism of oxo-active site formation in Cu-ZSM-5.

Oxygen precursor to the reactive intermediate in methanol synthesis by Cu-ZSM-5

Copper-exchanged zeolites can continuously and selectively catalyze the partial oxidation of methane to methanol using only oxygen and water at low temperatures, but the genesis and nature of the active sites are currently unknown. Herein, we demonstrate that this reaction is catalyzed by a [Cu-O-Cu]2+ motif that forms via a hypothesized proton-aided diffusion of hydrated Cu ions within the cages of SSZ-13 zeolites. While various Cu configurations may be present and active for methane oxidation, a dimeric Cu motif is the primary active site for selective partial methane oxidation. Mechanistically, CH4 activation proceeds via rate-determining C-H scission to form a surface-bound C1 intermediate that can either be desorbed as methanol in the presence of H2O/H+ or completely oxidized to CO2 by gas-phase O2. High partial oxidation selectivity can be obtained with (i) high methane and water partial pressures and (ii) maximizing Cu dimer formation by using zeolites with high Al content and low Cu loadings.

Continuous Partial Oxidation of Methane to Methanol Catalyzed by Diffusion-Paired Copper Dimers in Copper-Exchanged Zeolites.

C1 chemistry, which is the catalytic transformation of C1 molecules including CO, CO2 , CH4 , CH3 OH, and HCOOH, plays an important role in providing energy and chemical supplies while meeting environmental requirements. Zeolites are highly efficient solid catalysts used in the chemical industry. The design and development of zeolite-based mono-, bi-, and multifunctional catalysts has led to a booming application of zeolite-based catalysts to C1 chemistry. Combining the advantages of zeolites and metallic catalytic species has promoted the catalytic production of various hydrocarbons (e.g., methane, light olefins, aromatics, and liquid fuels) and oxygenates (e.g., methanol, dimethyl ether, formic acid, and higher alcohols) from C1 molecules. The key zeolite descriptors that influence catalytic performance, such as framework topologies, nanoconfinement effects, Bronsted acidities, secondary-pore systems, particle sizes, extraframework cations and atoms, hydrophobicity and hydrophilicity, and proximity between acid and metallic sites are discussed to provide a deep understanding of the significance of zeolites to C1 chemistry. An outlook regarding challenges and opportunities for the conversion of C1 resources using zeolite-based catalysts to meet emerging energy and environmental demands is also presented.

/pdf/applications-of-zeolites-to-c1-chemistry-recent-advances-1llq7ch3ru.pdf

Applications of Zeolites to C1 Chemistry: Recent Advances, Challenges, and Opportunities

Methane selective oxidation to methanol by metal-exchanged zeolites: a review of active sites and their reactivity

Methane activation is usually assumed to take place on top of metal surfaces or metal clusters. It can also occur at the metal–support interface in metal-supported catalysts with reducible oxides, such as CeO2. In the present work, we exploit density functional theory with an additional Hubbard-like parameter (DFT + U) to calculate the activation of methane at an O site interfacing a Ni4 metal cluster on a support, CeO2(111) surface. Two reaction routes, namely, radical and nonradical routes, are taken into account. We show that the nonradical route is favored with an apparent activation energy of 18.1 kcal/mol, which is lower than that for the radical route by 15.0 kcal/mol. In the nonradical route, the formation of a four-centered transition-state structure is observed while a C–H bond of methane is being cleaved to form an OH moiety and a CH3 fragment that is being bound to the interfacial Ni atom. It is also found that the interfacial O atoms are out of the CeO2 surface plane with Ce–O bond distances ...

Methane Activation at the Metal–Support Interface of Ni4–CeO2(111) Catalyst: A Theoretical Study

DFT exploration of active site motifs in methane hydroxylation by Ni-ZSM-5 zeolite

Zn-ZSM-5 zeolite is a promising catalyst that activates methane at room temperature without the need of a high-temperature pre-oxidation step, which is required for Fe- and Cu-ZSM-5 to form Fe- and...

Room-Temperature Activation of Methane and Direct Formations of Acetic Acid and Methanol on Zn-ZSM-5 Zeolite: A Mechanistic DFT Study

Fe- and Cu-exchanged zeolites are known to oxidize methane directly to methanol at low temperature and have been intensively discussed in recent literature studies including theoretical works based...

Muhammad Haris Mahyuddin

Papers

Methane selective oxidation to methanol by metal-exchanged zeolites: a review of active sites and their reactivity

Methane Activation at the Metal–Support Interface of Ni4–CeO2(111) Catalyst: A Theoretical Study

DFT exploration of active site motifs in methane hydroxylation by Ni-ZSM-5 zeolite

Room-Temperature Activation of Methane and Direct Formations of Acetic Acid and Methanol on Zn-ZSM-5 Zeolite: A Mechanistic DFT Study

Novel mechanistic insights into methane activation over Fe and Cu active sites in zeolites: A comparative DFT study using meta-GGA functionals