Gas Phase Catalytic Hydrogenation of C4 Alkynols over Pd/Al₂O₃

• Main Authors: Alberto González-Fernández, Chiara Pischetola, Fernando Cárdenas-Lizana
• Format: Article
• Language: English
• Published: MDPI AG 2019-11-01
• Series: Catalysts
• Subjects: gas phase hydrogenation; alkynols; 3-butyn-1-ol; 3-butyn-2-ol; 2-methyl-3-butyn-2-ol; alkenols; triple bond electron charge; pd/al₂o₃
• Online Access: https://www.mdpi.com/2073-4344/9/11/924

Alkenols are commercially important chemicals employed in the pharmaceutical and agro-food industries. The conventional production route via liquid phase (batch) alkynol hydrogenation suffers from the requirement for separation/purification unit operations to extract the target product. We have examined, for the first time, the continuous gas phase hydrogenation (<i>P</i> = 1 atm; <i>T</i> = 373 K) of primary (3-butyn-1-ol), secondary (3-butyn-2-ol) and tertiary (2-methyl-3-butyn-2-ol) C₄ alkynols using a 1.2% wt. Pd/Al₂O₃ catalyst. <i>Post</i>-TPR, the catalyst exhibited a narrow distribution of Pd^&#948;- (based on XPS) nanoparticles in the size range 1-6 nm (mean size = 3 nm from STEM). Hydrogenation of the primary and secondary alkynols was observed to occur in a stepwise fashion (-C&#8801;C- &#8594; -C=C- &#8594; -C-C-) while alkanol formation via direct -C&#8801;C- &#8594; -C-C- bond transformation was in evidence in the conversion of 2-methyl-3-butyn-2-ol. Ketone formation via double bond migration was promoted to a greater extent in the transformation of secondary (<i>vs.</i> primary) alkynol. Hydrogenation rate increased in the order primary &lt; secondary &lt; tertiary. The selectivity and reactivity trends are accounted for in terms of electronic effects.