Facet-dependent synthesis of H2O2 from H2 and O2 over single Pt atom-modified Pd nanocrystal catalysts

Hydrogen peroxide (H2O2) is one of the most valuable clean energy sources with a rapidly growing requirement in industry and daily life. The direct synthesis of H2O2 from hydrogen and oxygen is considered to be an economical and environmentally friendly manufacturing route to replace the traditional anthraquinone method, although it remains a formidable challenge owing to low H2O2 selectivity and production. Here, we report a catalyst consisting of Pd(111) nanocrystals on TiO2 modified with single Pt atoms (Pt1Pd(111)/TiO2), which displays outstanding reactivity, producing 1921.3 μmol of H2O2, a H2 conversion of 62.2% and H2O2 selectivity of 80.3% over 30 min. Kinetic and isotope experiments confirm that the extraordinary catalytic properties are due to stronger H2 activation (the rate-determining step). DFT calculations confirm that Pt1Pd(111) exhibits lower energy barriers for H2 dissociation and two-step O2 hydrogenation, but higher energy barriers for side reactions than Pt1Pd(100), demonstrating clear facet dependence and resulting in greater selectivity and amount of H2O2 produced.

Hydrogen Peroxide Versus Hydrogen Generation at Bipolar Pd/Au Nano-catalysts Grown into an Intrinsically Microporous Polyamine (PIM-EA-TB)

Binding of PdCl42− into the polymer of intrinsic microporosity PIM-EA-TB (on a Nylon mesh substrate) followed by borohydride reduction leads to uncapped Pd(0) nano-catalysts with typically 3.2 ± 0.2 nm diameter embedded within the microporous polymer host structure. Spontaneous reaction of Pd(0) with formic acid and oxygen is shown to result in the competing formation of (i) hydrogen peroxide (at low formic acid concentration in air; with optimum H2O2 yield at 2 mM HCOOH), (ii) water, or (iii) hydrogen (at higher formic acid concentration or under argon). Next, a spontaneous electroless gold deposition process is employed to attach gold (typically 10- to 35-nm diameter) to the nano-palladium in PIM-EA-TB to give an order of magnitude enhanced production of H2O2 with high yields even at higher HCOOH concentration (suppressing hydrogen evolution). Pd and Au work hand-in-hand as bipolar electrocatalysts. A Clark probe method is developed to assess the catalyst efficiency (based on competing oxygen removal and hydrogen production) and a mass spectrometry method is developed to monitor/optimise the rate of production of hydrogen peroxide. Heterogenised Pd/Au@PIM-EA-TB catalysts are effective and allow easy catalyst recovery and reuse for hydrogen peroxide production.

Graphical abstract