Role of Ligand in the Selective Production of Hydrogen from Formic Acid Catalysed by the Mononuclear Cationic Zinc Complexes [(L)Zn(H)]+ (L=tpy, phen, and bpy)1. Issue 42 (3rd July 2019)

• Record Type: Journal Article
• Authors: Piacentino, Elettra L.; Parker, Kevin; Gilbert, Thomas M.; O'Hair, Richard A. J.; Ryzhov, Victor
• Is Part Of: Chemistry. Volume 25:Issue 42(2019)
• Page Start: 9959
• Page End: 9966
• Publication Date: 2019-07-03
• Subjects: density functional calculations -- formic acid -- hydrogen storage -- mass spectrometry -- zinc catalysts; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201901360
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: A series of zinc‐based catalysts was evaluated for their efficiency in decomposing formic acid into molecular hydrogen and carbon dioxide in the gas phase using quadrupole ion trap mass spectrometry experiments. The effectiveness of the catalysts in the series [(L)Zn(H)] +, where L=2, 2′:6′, 2′′‐terpyridine (tpy), 1, 10‐phenanthroline (phen) or 2, 2′‐bipyrydine (bpy), was found to depend on the ligand used, which turned out to be fundamental in tuning the catalytic properties of the zinc complex. Specifically, [(tpy)Zn(H)] + displayed the fastest reaction with formic acid proceeding by dehydrogenation to produce the zinc formate complex [(tpy)Zn(O2 CH)] + and H2 . The catalysts [(L)Zn(H)] + are reformed by decarboxylating the zinc formate complexes [(L)Zn(O2 CH)] + by collision‐induced dissociation, which is the only reaction channel for each of the ligands used. The decarboxylation reaction was found to be reversible, since the zinc hydride complexes [(L)Zn(H)] + react with carbon dioxide yielding the zinc formate complex. This reaction was again substantially faster for L=tpy than L=phen or bpy. The energetics and mechanisms of these processes were modelled using several levels of density functional theory (DFT) calculations. Experimental results are fully supported by the computational predictions. Abstract : Yes, we ant : Zn complexes, in the form of [(L)Zn(H)] +, in which L is a nitrogen‐containing ligand, were found to be effective catalysts for the selective decomposition of formic acid in the gas phase (see graphic). Computational evaluations of reaction energetics and transition states agreed with the experimental reaction efficiencies. The study shows that combining abundant metals and simple ligands can create more efficient and affordable catalysts.