Remarkable Effect of Electric Field Direction on Electrothermally Catalytic Selective Oxidation of (Meth)acrolein...

Catalytic partial oxidation of unsaturated aldehydes to acids still remains a significant challenge because of the difficult control of product selectivity. Herein, we propose a promising electrothermally catalytic process for selective oxidation of probing (meth)acrolein to (meth)acrylic acid on a Keggin-type phosphomolybdovanadic heteropolyacid modified with pyridine (Py-HPAV). It is discovered that the electric field direction imposed on the catalyst bed significantly affects catalytic selectivity across modified and supported heteropolyacid samples, with a supreme difference of 14%, resulting from the changes of redox property, surface adsorption/desorption behavior, and orientation of active sites. Structure-activity relationship analysis reveals that the reduction of Mo6+ and V5+ to Mo5+ and V4+, respectively, will be promoted in a linear proportion with the intensified electric field, which correspondingly influences the transformative rate and selectivity. Detailed mechanistic and kinetic studies support the effect of electric field direction on aldehyde adsorption, formation, and conversion of intermediate species and acid desorption. Additional theoretical computations confirm that the opposite direction between the electric field and molecular dipole moment of adsorbed aldehyde/acid results in low adsorption and desorption energies, thereby suppressing the undesired overoxidation. In addition, the electric field direction will also influence the orientation of catalytically active Mo-O-V sites in comparison to the feed stream, which consequently affects the contact between the reactants and active sites. This work offers a valuable strategy to control the catalytic selectivity in the oxidation of unsaturated aldehydes to acids under an applied electric field.