A facile synthesis strategy for Al-SBA-15 with a high density of acid sites via a neutral pathway for efficient hydrodeoxygenation of levulinic acid to γ-valerolactone.

Al-containing SBA-15 (Al-SBA-15) has shown great potential as a catalyst for hydrodeoxygenation (HDO); however, the limited efficiency of aluminum (Al) incorporation under highly acidic conditions is a key challenge in the formation of Al-SBA-15. Herein, we report a facile, neutral strategy aimed at achieving the composition of Al-SBA-15 by employing aluminum citrate (Al-Cit) as both an Al source and an assembly-assisting agent. In this unique procedure, the citrate anion formed a stable, water-soluble complex with Al3+, which suppressed its hydrolysis and maintained the Al species in its reactive state during synthesis. Meanwhile, the carboxylic groups of Al-Cit engaged in hydrogen bonding with the PEO segments of the P123(PEO20PPO70PEO20) template and coordinated with the silicate species, resulting in the assembly of mesoporous material. Al was incorporated into the silica framework as tetrahedrally coordinated Al(IV) under neutral conditions due to this dual function. The samples obtained by this procedure showed highly ordered mesoporosity. In addition, the combined results of XRD, FT-IR, ICP-OES, XPS, and 27Al MAS NMR confirmed that the obtained Al-SBA-15 contained a much higher amount of framework Al species than the conventional acid-synthesized sample. The neutral method generated Al-SBA-15 with superior texture, including abundant acid sites, high mesoporous surface area (MSA), and uniform pores. Moreover, the acid sites in Al-SBA-15 facilitated the enhanced dispersion of Ni species and higher HDO efficiency during the HDO of levulinic acid (LA) to γ-valerolactone (GVL).