Exergy valorization of a water electrolyzer and CO hydrogenation tandem system for hydrogen and methane production.

In this work, we introduce a water electrolysis and CO hydrogenation tandem system which focuses on methane generation. The concept consists of a water electrolyzer thermally coupled to a CO hydrogenation reactor, where the power required to generate hydrogen comes from renewable energy. A thermodynamic analysis of the tandem system was carried out.

Oxidative reactions of tetrametal Pd(0)...Mo(II)-Mo(II)...Pd(0) clusters: electrochemical communication of two Pd(0) centers through the Mo(2) moiety and oxidative formation of a Pd(I)-Mo(II)-Mo(II)-Pd(I) array.

Reaction of Mo(2)(pyphos)(4) (1) (pyphos = 6-diphenylphosphino-2-pyridonate) with Pd(dba)(2) (dba = dibenzylideneacetone) afforded the Pd(0) complex Mo(2)Pd(2)(pyphos)(4) (2) which has two Pd(0) centers at both axial positions of the Mo(2) core. The unsaturated Pd(0) centers of 2 were coordinated with donor molecules such as olefins, acetylenes, isonitriles, carbon monoxide, and triphenylphosphine to give the corresponding adducts, Mo(2)Pd(2)(pyphos)(4)(L)(2) (3a: L = acrylonitrile, 3b: L = fumaronitrile, 3c: L = tetracyanoethylene, 3d: L = diisopropyl fumarate, 3e: L = diethyl fumarate, 3f: L = dimethyl fumarate, 3g: L = dimethyl maleate, 3h: L = 2,6-xylylisocyanide, 3i: L = tert-butylisocyanide, 3j: L = dimethyl acetylenedicarboxylate, 3k: L = 1,4-benzoquinone, 3l: L = 1,4-naphthoquinone, 3m: L = carbon monooxide, and 3n: L = triphenylphosphine). Oxidative 1,4-addition of ArSSAr and benzoyl peroxide to the Pd(0) centers of 2 afforded the corresponding Pd(I) complexes Mo(2)Pd(2)(SAr)(2)(pyphos)(4) (7a: Ar = C(6)H(5), 7b: Ar = 4-Me(3)CC(6)H(4), 7c: Ar = 4-MeC(6)H(4), 7d: 4-NO(2)C(6)H(4)) and Mo(2)Pd(2)(OCOPh)(2)(pyphos)(4) (9).

Linear metal-metal-bonded tetranuclear M-Mo-Mo-M complexes (M = Ir and Rh): oxidative metal-metal bond formation in a tetrametallic system and 1,4-addition reaction of alkyl halides.

Reaction of Mo2(pyphos)4 (1) with [MCl(CO)2]2 (M = Ir and Rh) afforded linear tetranuclear complexes of a formula Mo2M2(CO)2(Cl)2(pyphos)4 (2, M = Ir; 3, M = Rh). X-ray diffraction studies confirmed that two "MCl(CO)" fragments are introduced into both axial sites of the Mo2 core in 1 and coordinated by two PPh2 groups in a trans fashion, thereby forming a square-planar geometry around each M(I) metal. Treatment of 2 and 3 with an excess amount of tBuNC and XylNC induced dissociation of the carbonyl and chloride ligands to yield the corresponding dicationic complexes [Mo2M2(pyphos)4(tBuNC)4](Cl)2 (5a, M = Ir; 6a, M = Rh) and [Mo2M2(pyphos)4(XylNC)4](Cl)2 (7, M = Ir; 8, M = Rh).

Unique oxidative metal-metal bond formation of linearly aligned tetranuclear Rh-Mo-Mo-Rh clusters.

Reaction of Mo2(pyphos)4 (1) with [RhCl(CO)2]2 followed by treatment of excess amounts of tBuNC resulted in the clean formation of [Mo2Rh2(tBuNC)4(pyphos)4](X)2 (4a; X = Cl). The X-ray diffraction study as well as spectroscopic analyses of 4c (X = BPh4) implied that there is no direct sigma-bonding interaction between each Rh(I) atom and the Mo2 core. Each Rh(I) atom in 4 can be oxidized concurrently by 2 equiv of [Cp2Fe]PF6 to afford [Mo2Rh2(Cl)2(tBuNC)4(pyphos)4](PF6)2 (5) along with the formation of two Mo-Rh(II) single bonds and the reduction of the bond orders of the Mo-Mo moiety.