Structure–Activity Relationship of Magnesium Tin Fluoride Catalysts (MSF) with Varying Sn Doping Levels in the Reduction of p-Nitrophenol (PNP) to p Aminophenol (PAP)

Abstract

The catalytic reduction of toxic p-nitrophenol (PNP) into industrially valuable p-aminophenol (PAP) requires efficient, non-noble metal catalysts to ensure sustainability and cost-effectiveness. In this study, Magnesium Tin Fluoride (MSF) catalysts were synthesized via a fluorolytic sol-gel method using magnesium methoxide and tin(II) chloride dihydrate as precursors to ensure high phase purity and minimize residual anion interference. The effects of varying Sn doping levels (0 to 0.150 mol) on the physicochemical properties were systematically investigated using XRD, FTIR, BET, and SEM-EDX. XRD analysis confirmed the retention of the tetragonal MgF₂ structure (JCPDS No. 70-2269), while subtle shifts in diffraction peaks indicated the successful incorporation of Sn⁴⁺ into the MgF₂ lattice. Nitrogen adsorption-desorption revealed that Sn doping significantly enhanced the specific surface area, peaking at 36.096 m²/g for the MS4F sample (0.10 mol Sn), compared to only 10.391 m²/g for the undoped MS0F. Catalytic testing showed that MS4F achieved an optimal PNP conversion of 98.55% and a PAP yield of 72.46%. The enhanced performance is attributed to the synergistic effect of increased surface area and optimized Brønsted acidity provided by hydroxyl groups, which facilitate electron transfer during the reduction process. However, excessive doping (MS5F) led to particle agglomeration and a subsequent decline in catalytic efficiency. This study establishes a clear structure–activity relationship, demonstrating that precise control of Sn concentration is vital for tailoring the structural integrity and reactivity of fluoride-based catalysts.

HIGHLIGHTS

Highlights

• High-purity Magnesium Tin Fluoride (MSF) catalysts were successfully developed via a strategic sol-gel method using magnesium methoxide precursors to ensure phase purity and minimize ionic interference.
• Systematic Sn-doping (0 - 0.150 mol) effectively tailored the catalyst's physicochemical properties, tripling the specific surface area from 10.391 to 36.096 m²/g.
• The MS4F catalyst (0.10 mol Sn) achieved a rem2arkable 98.55% conversion of toxic p-nitrophenol (PNP) and a 72.46% yield of industrially valuable p-aminophenol (PAP).
• This study establishes a clear correlation between dopant concentration, surface acidity (Lewis and Brønsted), and reactivity, providing critical insights into the synergy required for efficient electron transfer.
• These findings highlight the potential of non-noble metal fluoride catalysts as cost-effective and robust alternatives for green chemical synthesis and environmental remediation.

GRAPHICAL ABSTRACT