A new strategy for fabricating an optimal porous strong base was reported for the first time. Magnesium and zinc acetates were mixed by microwave irradiation followed by carbonization at 823 K. Zn incorporation enabled the magnesia nanoparticles to have more surface defects, and about 80% of the basic sites were strong ones with the ability to capture CO₂ at 473 K, which is the highest proportion to date. These porous binary metal oxides had large surface areas between 130–296 m² g⁻¹.