Complex sentence: In 1838 he was recognised as an excellent modeller, presenting his work at a local exhibition at Mechelen/Malines that so impressed the minister Rogier who was opening the exhibition that he arranged a place for Walschaerts at Liège University.
Split into simpler sentences: In 1838 he was recognised as an excellent modeller, presenting his work at a local exhibition in Mechelen. Minister Rogier, who opened the exhibition, was so impressed that he arranged a place for Walschaerts at Liège University.