From Waste to Green Applications: The Use of Recovered Gold and Palladium in Catalysis

Abstract

The direct use in catalysis of precious metal recovery products from industrial and consumer waste is a very promising recent area of investigation. It represents a more sustainable, environmentally benign, and profitable way of managing the low abundance of precious metals, as well as encouraging new ways of exploiting their catalytic properties. This review demonstrates the feasibility and sustainability of this innovative approach, inspired by circular economy models, and aims to stimulate further research and industrial processes based on the valorisation of secondary resources of these raw materials. The overview of the use of recovered gold and palladium in catalytic processes will be complemented by critical appraisal of the recovery and reuse approaches that have been proposed.

Keywords: TWC; WEEE; catalysis; circular economy; critical metals; gold; green processes; palladium; recycling.

Figure 1

Periodic table depicting the pollution impact caused by mining of various elements. Reproduced with permission from [22].

Figure 2

Comparison of the amount of various metals yielded from recycled mobile phones compared to primary ore [35].

Figure 3

Flowsheets of (A) precious metals being recycled from WEEE by a pyrometallurgical process, reproduced with permission from [39] and (B) simplified plan of the Umicore integrated smelter-refinery plant, reproduced with permission from [40].

Figure 4

Structures of a MOF based on Ca²⁺ and Cu²⁺ employed for gold recovery (left), and its gold recovery product (right). Reproduced with permission from [68].

Figure 5

Cyclisation of 4-pentyn-1-ol catalysed by recovered gold, Reproduced with permission from [68].

Figure 6

Polyamide adsorbent used for gold recovery and catalysis. PA12 is the unused adsorbent, PA12-Au is the adsorbent after gold recovery. NaBH₄ indicates the Au⁰ loaded PA12 after reduction by NaBH₄. Reproduced with permission from [69,70].

Figure 7

Chitin nanofibrous membrane employed for gold recovery and catalysis. Reproduced with permission from [71].

Figure 8

Palladium-loaded UiO-55-Pyta MOF employed as a Suzuki–Miyaura catalyst [97].

Figure 9

Micellar back-extraction of recovered palladium [98]. Reproduced with permission [98].

Figure 10

Palladium recovery enabled by a Glaser coupling to yield a cross-linked gel, Reproduced with permission from [99].

Figure 11

Activity of a palladium-loaded aerogel as a Suzuki–Miyaura catalyst, Reproduced with permission from [99].

Figure 12

Recovery of palladium using Me₂dazdt·2I₂, Reproduced with permission from [100,102].

Figure 13

Expanded recovery products derived from Me₂dazdt·I₂, Reproduced with permission from [107].

Figure 14

Application of three-way catalyst (PW-TWC) material applied directly in milled form as a catalyst for the reduction of nitroarenes, Reproduced with permission from [109].

Figure 15

Application of powdered waste three-way catalyst (PW–TWC) materials as in-flow alkene hydrogenation catalysts. Residence time (τ = catalyst cartridge volume/flow rate), Reproduced with permission from [110].

Figure 16

Application of PW-TWC material as an in-flow tandem cyclisation/hydrogenation catalyst. Residence time (τ = catalyst cartridge volume/flow rate, Reproduced with permission from [111].