“Click” Dendrimer‐Stabilized Nanocatalysts for Efficient Hydrogen Release upon Ammonia‐Borane Hydrolysis

Abstract

Ammonia‐borane is one of the most convenient sources of H2 upon hydrolysis under ambient conditions, but the reaction requires a good catalyst to become efficient. Here, H2 production upon hydrolysis of ammonia‐borane is catalyzed by late transition‐metal nanoparticles (NPs). These NPs are stabilized by a first‐ or second‐generation “click” dendrimer containing, respectively 27 and 81 terminal triethylene glycol termini and 9 resp. 27 1,2,3‐triazole intradendritic ligands. No significant dendritic effects were observed, however. The noble‐metal NPs are as expected much more efficient catalysts than the first‐raw transition‐metal NPs, and Rh and PtNPs are the most catalytically active NPs. In the presence of NaOH, however, the reactivity is boosted for all these “click” dendrimer‐stabilized transition‐metal NP catalysts except for the PtNPs. The optimized NaOH concentration is 0.3 M NaOH per mol NH3BH3 for RhNPs. A TOF of up to 611 molnormalH2 molcatalyst−1 min−1 for RhNPs at 20 °C is obtained, which is one of the best results among the literature. Interestingly, the reaction with D2O provides a kinetic isotope effect of kD/kH=2.8 suggesting that O−H bond cleavage of water occurs in the rate‐limiting step. These experiments lead to a proposed mechanism for H2 evolution using the ammonia‐borane hydrolysis reaction.

Efficient “Click”‐Dendrimer‐Supported Synergistic Bimetallic Nanocatalysis for Hydrogen Evolution by Sodium Borohydride Hydrolysis

“…This is particularly critical for catalysis applications in which a robust linkage between the MNPs and the support would improve performances in terms of recovery and re‐use of the catalyst as well as inhibition of product contamination ,. This has been demonstrated in particular using functionalized carbon structures,, polymers,, and mesoporous organosilica ,. Dendrimers have been extensively used as supports in catalysis because they often exert the function of nanoreactor contributing to protect MNPs and inhibit their agglomeration.…”

“…Dendrimers have been extensively used as supports in catalysis because they often exert the function of nanoreactor contributing to protect MNPs and inhibit their agglomeration. It is noteworthy, however, that the reports on the uses of dendrimers as supports in hydrogen generation are rare,,, and there has been no report on the use of a dendrimer in the catalysis of NaBH 4 hydrolysis.…”

A Simple and Efficient Device and Method for Measuring the Kinetics of Gas‐Producing Reactions

“…This can be solved using on‐line gas chromatography (GC) or mass spectrometry (MS). But since these instruments are expensive, and require long calibration procedures, the most commonly used method today is still the trusted upside‐down glass burette . This requires only a beaker, a burette, and some water.…”

“…But since these instruments are expensive,and require long calibration procedures,the most commonly used method today is still the trusted upside-down glass burette. [4][5][6][7][8][9] This requires only ab eaker,aburette,a nd some water. However,t he results are less accurate,a nd the measurements are still timeconsuming and laborious.Recently,w hile studying H 2 evolution from ammonia borane hydrolysis for MAX-phase supported metal catalysts, we were faced with the task of measuring the temperature dependence of rate constants of aseries of catalytic reactions.Rather than slog our way through numerous calibration experiments and repetitions, [10] we developed as imple and efficient bench-top device that automates this analysis.Unlike the upside-down burette,o ur device measures the development and passage of gas bubbles rather than the displacement of water.A st he same device also controls the reaction temperature,i te nables af ast and accurate measurement of Arrhenius relations,g iving hundreds of data points from asingle experiment.Herein, we present the theoretical and physico-chemical foundation for this new device and method.…”

“…But since these instruments are expensive,and require long calibration procedures,the most commonly used method today is still the trusted upside-down glass burette. [4][5][6][7][8][9] This requires only ab eaker,aburette,a nd some water. However,t he results are less accurate,a nd the measurements are still timeconsuming and laborious.…”