Boosting the Production of Glycolic Acid from Formaldehyde Carbonylation via the Bifunctional PdO/ZSM-5 Catalyst

The carbonylation of formaldehyde offers a promising, cost-effective, and environmentally friendly method for synthesizing glycolic acid, a crucial monomer in biodegradable plastics. This study highlights the development and optimization of a bifunctional PdO/ZSM-5 zeolite catalyst for this process. Investigations via various spectroscopic techniques reveal that Pd species, predominantly in the form of PdO, enhance the CO activation, thereby boosting the formaldehyde carbonylation reaction rate significantly. The optimal catalytic performance was observed with a Pd-loading of 2 wt %. Notably, excessive Pd loading was found to impede the catalytic performance by overoccupying acid sites, thereby reducing its capacity to activate formaldehyde. The concurrent activation of formaldehyde and CO at the Bronsted acid site and the PdO site, respectively, through a Langmuir-Hinshelwood mechanism is key to the enhanced catalytic performance. These findings underscore the importance of CO activation in improving the formaldehyde carbonylation process, offering vital insights for catalyst optimization.