The technique of catalytic flow microreactor has been combined with the gas flow-through microcalorimetry to correlate the catalytic activity of supported heteropolyacids with both the acid strength of protons as well as the protons' accessibility. Multiwall carbon nanotubes (CNT) were used as a support for Keggin (H3PW12O40) and Wells-Dawson (H6P2W18O62) structured heteropolyacids, in order to produce catalysts combining high acidity from the parent acids with the inherent microporosity of the support. Prior to the catalytic tests, the obtained materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) and Raman spectroscopies as well as by the nitrogen adsorption-desorption analysis (BET). The latter technique confirmed overall improved porosity of the obtained materials. Upon testing for activity in the isopropyl alcohol dehydration, the supported Wells-Dawson catalysts turned out to be superior to both the Keggin-based materials, as well as to the unsupported H6P2W18O62. It has been found that the improvement of catalytic performance in the isopropanol conversion is mostly related to the increase of the accessibility of protons, rather than to the changes in the acid strengths.