A polyether polyol is formed by a method utilizing a carboxy-modified aluminum-based catalyst. The method includes providing an alkylene oxide, providing an initiator molecule having at least one alkylene oxide reactive hydrogen, and reacting the alkylene oxide with the initiator molecule in the presence of the catalyst. The ideal carboxy-modified aluminum based catalysts used herein are selected from the group of carboxy-modified aluminum phosphate catalysts, carboxy-modified aluminum phosphonate catalysts, and residues or mixtures thereof.