Investigating deposition sequence during synthesis of Pd/Al2O3 catalysts modified with organic monolayers. Issue 7 (2nd March 2022)

• Record Type: Journal Article
• Authors: Blanchette, Zachary; Zhang, Jing; Yazdi, Sadegh; Griffin, Michael B.; Schwartz, Daniel K.; Medlin, J. Will
• Is Part Of: Catalysis science & technology. Volume 12:Issue 7(2022)
• Page Start: 2306
• Page End: 2314
• Publication Date: 2022-03-02
• Subjects: Catalysis -- Periodicals; 541.395
• DOI: 10.1039/d1cy02131a
• Languages: English
• ISSNs: 2044-4753

Abstract

Abstract : Pd/Al2 O3 catalysts were modified with phosphonic acids through "metal-first" and "SAM-first" deposition sequences and evaluated for benzyl alcohol hydrodeoxygenation performance. SAM-first catalysts exhibited higher mass activities. Abstract : Modification of supported metal catalysts with self-assembled monolayers (SAMs) has been shown to improve selectivity and turnover frequencies (TOFs) for many catalytic reactions. However, these benefits are often accompanied by a decrease in overall mass activity due to partial blocking of active sites by the monolayers. Therefore, a potential method for increasing site accessibility is to deposit the active metal ( e.g., Pd) after deposition of a SAM modifier on the support material. In this work, Pd/Al2 O3 catalysts were synthesized using both a conventional, "metal-first" sequence in which the phosphonic acid (PA) SAM was deposited on Pd/Al2 O3 and a "SAM-first" technique in which the ligands were deposited onto the support prior to deposition of the metal. Although metal-first catalysts showed a significant increase in TOF during benzyl alcohol HDO, they exhibited only a modest increase in overall mass activity due to a decrease in the number of active sites. Meanwhile, SAM-first catalysts showed similar improvements in TOF and toluene selectivity but exhibited significantly improved HDO rates compared to metal-first catalysts. The rate increase was attributed to reduced site blocking as evidenced by CO chemisorption measurements. Additionally, analysis of catalysts having high Pd loadings using transmission electron microscopy (TEM) showed that SAM-first catalysts generally resulted in lower average particle sizes than traditionally modified and unmodified catalysts, suggesting that precoating the support surface with PAs changes the way that Pd is deposited during incipient wetness, leading here to improved activity.