Abstract
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
Highlights
Microporous environments are commonly employed for immobilisation of catalysts (i) to control/restrict reagent access, (ii) to enhance the accessible catalyst surface area, (iii) to recover and re-use catalysts, and (iv) to improve the catalyst micro-environment and catalyst efficiency for example for palladium catalysts [1]
A Clark probe was employed with Pd@polymers of intrinsic microporosity (PIMs)-EA-TB catalyst immobilised on a Nylon mesh substrate (8-mm-diameter disks, see “Experimental”)
With the Nylon substrate attached, the Clark probe allows both detection of oxygen consumption and detection of hydrogen production
Summary
Microporous environments are commonly employed for immobilisation of catalysts (i) to control/restrict reagent access, (ii) to enhance the accessible catalyst surface area, (iii) to recover and re-use catalysts, and (iv) to improve the catalyst micro-environment and catalyst efficiency for example for palladium catalysts [1]. Recently have wet-chemical applications for intrinsically microporous polymers emerged, for example, in electrochemistry [16, 17], in electrocatalysis with embedded molecular catalysts [18] or embedded nanoparticle catalysts for hydrogen production [19, 20], and for hydrogen peroxide [21] production. It is shown that Pd nanoparticles of typically 3.2-nm diameter are readily synthesised by absorption of PdCl42− followed by borohydride reduction These “guest” nanoparticles are active for hydrogen generation from formic acid due to PIMEA-TB not blocking the surface of the catalyst and effective permeation of formic acid. Both hydrogen production and oxygen consumption are monitored in situ with a Clark probe [33] (Fig. 1A) and employing Nylon mesh substrates. Nylon mesh from 75-μm diameter Nylon was purchased from Amazon.com (therpin reusable Nylon fine mesh food strainer bag)
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