De Deken was born in
Wilrijk. The son of Ludovicus De Deken and Maria-Theresia Van Dyck, he studied theology at the major
seminary of
Mechelen, then he made his
novitiate in the
Scheutist Fathers congregation in 1877. He was ordained Priest in June 1879 and took his final vows in March 1881. He was called to go to China to
christianize the population. He was first sent to the
Mission sui juris of I-li in
Chinese Turkestan (under the administration of the
Apostolic Vicariate of Kan-Su-Koukounor, now
Gansu). Scheutist fathers had been present in China since 1865 and wanted to expand their ministry to the northwest. Then followed a short period of study in Lanzhou to improve his Chinese. From April 1882 De Deken tried to evangelize the region of
Sichuan, making tours from the parish of
Kuldja. He stayed there until 1889. In 1889 De Deken joined a scientific expedition in
Turkestan of
Gabriel Bonvalot (accompanied by
Prince Henri of Orléans, as
botanist and photographer) along with his Chinese servant Bartholomeus. De Deken spoke Chinese and served as interpreter. The goal was to reach Shanghai via
Central Asia,
Tibet and
Tonkin, which was completed in September 1890. De Deken then separated from the explorers and headed on a boat to
Haiphong, eventually to return to France. These were the first modern European explorations penetrating the high Tibetan plateau, away from the roads which had been done before by
Father Huc and later
Nikolai Przewalski. This expedition was unprecedented, having traveled six thousand kilometers and recovering botanical collections that were subsequently studied at the
National Museum of Natural History in Paris. A year later Father De Deken left China and returned to the Scheutist Fathers
congregation in Brussels for a year. He published a description of his journey in a book (written in French) titled
Across Asia (1891). ==To Congo==