Ortho-para hydrogen conversion by highly scalable metal-organic frameworks

The catalytic ortho-para hydrogen conversion is a critical step in hydrogen liquefaction for its storage and transportation. While paramagnetic oxides are the standard catalysts, the most commercially prevalent is hydrous iron oxide (FeO(OH)). However, the inherently low catalytic activity of FeO(OH) poses substantial engineering constraints, hindering further improvements in liquefaction efficiency and process intensification. In this work, we evaluate the performance of three industrially scalable metal–organic frameworks (MOFs) as catalysts of ortho-para hydrogen conversion. Comparative analysis reveals that MIL-100(Fe), MIL-101(Fe), and ZIF-67(Co) exhibit substantially higher catalytic activity than conventional FeO(OH). We demonstrate a correlation between the accessibility of active sites and catalytic performance. Based on this insight, the activity of MIL-100(Fe) was reassessed and found to be approximately 30 times higher than previously recognized if optimal activation is applied, revealing its potential as a new scalable catalyst. Compared to the conventional FeO(OH) catalyst activated under optimal conditions, MIL-100(Fe) exhibited a 11-fold higher activity normalized by catalyst mass, which corresponds to a 4-fold higher activity normalized by catalyst-bed volume. These findings indicate promising avenues for the industrial implementation of MOF-based catalysts, with the potential to enhance the efficiency and reduce the cost of hydrogen liquefaction processes.