The ortho-para hydrogen conversion in the hydrogen liquefaction process is of great significance for the long-term storage and long-distance transportation of liquid hydrogen. This paper outlines the differences in properties between orthohydrogen and parahydrogen

reviews the research progress on the physical mechanisms and reaction kinetic models of the ortho-para hydrogen catalytic conversion process

and summarizes the performance of common catalysts. Lastly

three mainstream schemes for ortho-para hydrogen conversion are compared. The researches on internal physical mechanisms and reaction kinetic models explore the conversion process from microscopic and macroscopic perspectives

respectively. Due to the lack of experimental data

scholars have not yet formed a unified explanation on the surface characteristics of catalysts

which needs to be quantitatively validated. Furthermore

although nickel-based catalysts have higher catalytic efficiency

iron hydroxides and oxide catalysts would be the mainstream catalyst choices for ortho-para hydrogen conversion

taking into account the preparation

activation

deactivation of catalysts and the characteristics of the liquefier. Among the three mainstream ortho-para hydrogen conversion schemes

the hydrogen liquefaction process with continuous conversion has the lowest energy consumption and is the future direction. The relevant domestic researches are still in beginning stages and have great potential for development. This paper can provide theoretical guidance for the design and construction of ortho-para hydrogen catalytic conversion test benches.