Surface Coordination Engineered Single-Atom Catalysts toward Biomass Tandem Conversion

Single-atom catalysts (SACs) with explicit active sites have shown advantages in heterogeneous catalytic reactions; however, the optimization of their performance in multistep tandem reactions [e.g., hydrodeoxygenation-isomerization (HIS) reaction in biomass conversion] remains a formidable challenge. Herein, we report a metal–acid bifunctional catalyst that is featured with Ni single atoms immobilized into the montmorillonite (MMT) framework via isomorphous substitution, followed by surface acid modification. The optimized 0.4 wt % Ni/MMT-IA catalyst exhibits prominent catalytic performance toward one-pot HIS reaction of palmitic acid with an iso-alkanes yield of 80.3%, which is preponderant to the state-of-the-art catalysts. Furthermore, the obtained catalyst not only displays durability for 30 reaction cycles (240 h, 300 °C), but also demonstrates universality in HIS reactions of 10 bio-oils. By virtue of in situ spectroscopy characterizations and theoretical calculations, we substantiate a two-step consecutive reaction pathway, including *COOH hydrodeoxygenation and *COH hydroisomerization. The single-atom metal–Brønsted acid site (Niδ+-O(H)) serves as the intrinsic active center, which significantly promotes the rate-determining step (β-H scission of the carbonium ion intermediate), resulting in the extraordinarily high yield of iso-alkanes. This work provides a feasible method for the design and preparation of high-performance SACs, which shows prospective applications in biofuel synthesis.