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The hydrogenation of CO 2 to formic acid is an essential subject since formic acid is a promising hydrogen storage material and a valuable commodity chemical. In this study, we report for the first time the hydrogenation of CO 2 to formic acid catalyzed by a Pd 2+ catalyst, Pd-V/AC-air. The catalyst exhibited extraordinary catalytic activity toward the hydrogenation of CO 2 to formic acid. The TON and TOF are up to 4790 and 2825 h -1 , respectively, representing the top level among reported heterogeneous Pd catalysts. By combining a study of first-principles density functional theory with experimental results, the superiority of Pd 2+ over Pd 0 was confirmed. Furthermore, the presence of V modified the electronic state of Pd 2+ , thus promoting the reaction. This study reports the effect of metal valence and electronic state on the catalytic performance for the first time and provides a new prospect for the design of an efficient heterogeneous catalyst for the hydrogenation of CO 2 to formic acid., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Guaiacol is an important feedstock for producing various high-value chemicals. However, the current production route of guaiacol relies heavily on fossil resources. Using lignin as a cheap and renewable feedstock to selectively produce guaiacol has great potential, but it is a challenge because of its heterogeneity and inert reactivity. Herein, we discovered that La(OTf) 3 could catalyze the transformation of lignin with guaiacol as the only liquid product. In the reaction, La(OTf) 3 catalyzed the hydrolysis of lignin ether linkages to form alkyl-syringol and alkyl-guaiacol, which further underwent decarbonization and demethoxylation to produce guaiacol with a yield of up to 25.5 wt%, and the remaining residue was solid. In the scale-up experiment, the isolated yield of guaiacol reached up to 21.2 wt%. To our knowledge, this is the first work to produce pure guaiacol selectively from lignin. The bio-guaiacol may be considered as a platform to promote lignin utilization., Competing Interests: The authors declare no competing financial interests., (This journal is © The Royal Society of Chemistry.)