Generation of acidic sites in Al, Ga, In salts of molybdenum and tungsten Keggin-type heteropolyacids. DFT modeling and catalytic tests

•MePMo salts exhibit weak redox properties while MePW is not active in redox reaction.•Both types of salts MePW and MePMo are active in acidic reactions.•Acidic properties change in decreasing order HPW>GaPW>InPW>AlPW>>>HPMo>GaPMo>InPMo>AlPMo.•Theoretical predictions were confirmed by experimental results.