Ziegler-type hydrogenation catalysts made from group 8–10 transition metal precatalysts and AlR3 cocatalysts: A critical review of the literature

Ziegler-type hydrogenation catalysts (group 8–10 transition metal precatalysts plus AlR3 cocatalysts) are one of the most important families of industrial hydrogenation catalysts, especially for polymer hydrogenation. Despite their ∼40 year history of industrial use, there is a need for improved fundamental understanding in order to make further, rationally directed improvements in these catalysts. This review examines the existing literature on Ziegler-type hydrogenation catalysts, specifically: (i) the variables important to catalyst synthesis, (ii) the catalyst formation reaction mechanism, (iii) the compositional and structural nature of the active catalyst species, and (iv) the mechanism of catalytic hydrogenation. This review also (v) discusses the current approaches to the homogeneous versus heterogeneous catalysis question, with the goal of identifying if Ziegler-type hydrogenation catalysts are homogeneous (e.g., monometallic) versus heterogeneous (e.g., nanoclusters) as the true catalyst(s). A summary of the main insights from each section of the review is also given.

Ziegler-type hydrogenation catalysts (group 8–10 transition metal precatalysts plus AlR3 cocatalysts) are one of the most important families of industrial hydrogenation catalysts, especially for polymer hydrogenation. This review examines the existing literature on the subject of Ziegler-type hydrogenation catalysts, with an emphasis on catalyst preparation variables, if the true catalyst is homogeneous (monometallic) or heterogeneous (nanoclusters), and on approaches to the historically perplexing “it is homogeneous or heterogeneous catalysis?” question.Figure optionsDownload as PowerPoint slide