Aerobic Methanol Oxidation over Unsupported Nanoporous Gold: The Influence of an Added Base

Nanoporous Gold: From Structure Evolution to Functional Properties in Catalysis and Electrochemistry

Nanoporous gold (NPG) is characterized by a bicontinuous network of nanometer-sized metallic struts and interconnected pores formed spontaneously by oxidative dissolution of the less noble element from gold alloys. The resulting material exhibits decent catalytic activity for low-temperature, aerobic total as well as partial oxidation reactions, the oxidative coupling of methanol to methyl formate being the prototypical example. This review not only provides a critical discussion of ways to tune the morphology and composition of this material and its implication for catalysis and electrocatalysis, but will also exemplarily review the current mechanistic understanding of the partial oxidation of methanol using information from quantum chemical studies, model studies on single-crystal surfaces, gas phase catalysis, aerobic liquid phase oxidation, and electrocatalysis. In this respect, a particular focus will be on mechanistic aspects not well understood, yet. Apart from the mechanistic aspects of catalysis, best practice examples with respect to material preparation and characterization will be discussed. These can improve the reproducibility of the materials property such as the catalytic activity and selectivity as well as the scope of reactions being identified as the main challenges for a broader application of NPG in target-oriented organic synthesis.

Photocatalytic coatings based on a zinc(ii) phthalocyanine derivative immobilized on nanoporous gold leafs with various pore sizes

A series of singlet oxygen sensitizing hybrid materials is reported consisting of a zinc(ii) phthalocyanine (ZnPc) derivative immobilized on nanoporous gold leafs (npAu) with various pore sizes. The resulting photocatalytic coatings exhibit a thickness of around 100 nm and pore sizes between 9–50 nm. Herein, we report the synthesis and characterization of those hybrid materials which were synthesized by functionalization of npAu leafs by an azide terminated alkanethiol self-assembled monolayer (SAM) and subsequent copper catalyzed azide–alkyne cycloaddition (CuAAC). The characterization of the samples morphology included scanning electron microscopy (SEM), UV-Vis spectroscopy as well as energy dispersive X-ray spectroscopy (EDX). The morphology–reactivity relationship was investigated employing the hybrid photocatalysts in the photooxidation of diphenylisobenzofuran (DPBF) as selective singlet oxygen quencher. An increasing photocatalytic activity was found for smaller pore sizes up to 15 nm, due to the gain in specific surface area concomitant with an increasing amount of immobilized photosensitizer, completely dominating the effect of the higher spectral overlap caused by the shift of the plasmon resonance of npAu, until mass transport and diffusion limitation gets predominant for pore sizes below 15 nm.

A series of hybrid materials consisting of a zinc(ii) phthalocyanine derivative immobilized on nanoporous gold leafs with various pore sizes was prepared and investigated regarding its singlet oxygen sensitization activity.

Impact of photosensitizer orientation on the distance dependent photocatalytic activity in zinc phthalocyanine–nanoporous gold hybrid systems

The distance dependency of the photocatalytic activity in zinc phthalocyanine–nanoporous gold hybrid systems was investigated revealing the importance of photosensitizer orientation in novel hybrid-based photocatalysts.