For over a century, Heusler alloys (X₂YZ; X, Y: transition metals, Z: typical metals) have attracted attention as magnetic materials. Nowadays, they are also popular as thermoelectric and shape memory materials. However, until very recently, Heusler alloys had been almost unknown as catalysts. We conceived that they could be ideal candidates for catalysts because (1) they have so many elemental sets and (2) they can be partially substituted with other elements (e.g. X₂YZ_1–xZ’_x) in many cases. We first investigated a variety of Heusler alloys as catalysts and then discovered effective catalysts without precious metals for the selective hydrogenation of alkynes based on the aforementioned feature (1) and demonstrated a systematic tuning of catalytic properties by applying the feature (2). Heusler alloy catalysts have also recently been studied by other groups; hence, this traditional alloy group is becoming a new stream in terms of catalysis. In this article, we review the current progress on Heusler alloy catalysts and describe their future prospects. Graphical Abstract

Intermetallic compounds have attracted research attention in catalysis because of their unique catalytic properties. Recently, a group of intermetallic compounds, referred to as Heusler alloys (X₂YZ), has been investigated as new catalysts. In this study, catalytic properties of 14 Heusler alloys with X = Fe, Co, Ni, or Cu; Y = Ti, Mn, or Fe; Z = Al, Si, Ga, Ge, or Sn for the steam reforming of methanol were examined. Co₂TiAl and Ni₂TiAl alloys exhibited relatively high H₂ production rates because of the formation of fine particles via the selective oxidation of Ti. X₂MnZ alloys exhibited high CO₂ selectivity because of a water-gas shift reaction catalyzed by using MnO that was formed during the reaction. Crystal phases, surface microstructures, and surface compositions of most alloys were changed because of the reaction, and the formation of fine particles possibly assisted in the observation of catalytic activity. Heusler alloys can be beneficial as catalyst precursors by the selection of appropriate elemental sets depending on target reactions.