On thermal stability and decomposition mechanisms of aromatic diamines employed as links in novel Pt nanoparticle network catalysts

In-operando FTIR study of ligand-linked Pt nanoparticle networks employed as catalysts in hydrogen gas micro sensors

“…Since PDA was deposited in an equimolar ratio to the amount of Pt during synthesis, a C : Pt ratio of 6 : 1 would be expected if the carbon content represented only PDA (C 6 H 8 N 2 ). The excess carbon is probably due to cyclohexanone residues from synthesis, also observed by TPD of freshly prepared Pt-PDA 6 and indicated by the presence of a weak ν (C O) band around 1700 cm −1 in FTIR ( cf. Fig.…”

“…A recent study on thermally induced decomposition of PDA-linked Pt NP networks by temperature-programmed desorption spectroscopy (TPD) in vacuum identified three different bonding configurations of PDA in freshly synthesized Pt-PDA (with 0, 1, or 2 dative NH 2 bonds to Pt) which differed with respect to thermal stability. 6 It was demonstrated that only the thermally most stable PDA species with two Pt bonds (double-bonded) is relevant for the structural stability of the Pt NP network. Therefore, in the present work, the maximum catalyst temperature during activation (180 °C) was kept below the onset of thermally induced decomposition of double-bonded PDA species reported at 200 °C, but above the onset of decomposition of single-bonded PDA.…”

“…It is nearby to assume that these residues stabilize the mesoporous, sponge-like Pt nanostructure. Furthermore, their presence indicates that in addition to hydrogenolysis reactions with solely volatile products (benzene, aniline, NH 3 ), 6 there must be at least one other relevant route of thermally induced PDA decomposition, probably similar to that identied by Huang et al for monofunctional aromatic and cycloaliphatic amines adsorbed on Ni surfaces which formed partially dehydrated polymeric layers and carbides. 15,16,18 Besides PDA, other bifunctional ligands were also used for Pt NP network synthesis in the present study (ligands BEN, DAN, DATER, and DACH as detailed in the experimental section).…”

“…In fact, a Pt-catalyzed cleavage of C-N bonds via hydrogenolysis reactions, reported for the thermally induced decomposition of aniline, [15][16][17] was previously found to be relevant for the decomposition of PDA in Pt-PDA, too. 6 The major decomposition products NH 3 , aniline and benzene are highly volatile. In accordance, the in operando FTIR data do not show any ngerprints of residual fragments or decomposition products of PDA in the catalyst.…”

“…Three-dimensional, microporous networks of Pt nanoparticles (NP) linked by diamine molecules recently turned out to be promising candidates for application as catalysts in H 2 microsensors. [1][2][3][4][5][6] Such networks have been synthesized from Pt NP with diameters of less than 2 nm and a selection of cycloaliphatic and various aromatic diamines, the choice of which allowed for tuning the average inter-particle distance within the networks in the range 1-2 nm. 4 Designed to offer a high spatial density of Pt surface sites, these novel materials generate a signicant heat tone from catalytic combustion of even minute amounts of hydrogen in air which can be exploited, e.g., by thermoelectrical sensor designs.…”