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A Tian-Calvet heat-flux microcalorimeter system is described for measurement of heats of adsorption and reaction on solid surfaces. Heat-flux signals are measured in transducer assemblies consisting of several hundred Seebeck-effect thermoelements connected in series, and arranged in a thimble configuration. These transducers surround quartz calorimeter cells connected to a high-vacuum, volumetric adsorption system, The sensitivity of the calorimeter can be calibrated with a Joule-effect device or by measurement of heats of adsorption for known processes. Microcalorimetric measurements have been conducted at temperatures from 300 to 473 K, and operation at temperatures from about 200 to 573 K is possible. Calorimeter cells are described that facilitate sample handling under controlled atmosphere conditions, allowing studies of freshly treated materials and samples that have been exposed to catalytic reaction conditions.

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Titanate nanotubes (TiNT) were synthesized by hydrothermal method and used as support of rhodium nanoparticles. Results of X-Ray diffraction (XRD) and Raman spectroscopy of TiNT revealed its structure of Na 2 Ti 3 O 7 , while the results of Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and physisorption of N 2 confirmed the multilayer nanotubular morphology with external diameter of ∼ 12 nm, length > 100 nm and a BET surface area of 195 m 2 g À 1 . The TEM analysis of the rhodium supported sample (Rh/TiNT) showed evidence of small (∼ 1 nm) and highly dispersed rhodium particles. Results of X-Ray Photoelectron Spectroscopy (XPS) revealed a strong electronic interaction between TiNT and Rh sites. The catalytic activity of Rh/TiNT for the hydrogenation of CO 2 to formic acid at moderate temperature (∼ 40°C) and atmospheric pressure was demonstrated as evidenced by results of Mass Spectrometry (MS) and in-situ Diffuse Reflectance Infrared with Fourier Transform Spectroscopy (DRIFTS). The in-situ studies showed active surface species bonded to support sites and to rhodium sites. It is proposed that under H 2 atmosphere, Na + cations near to Rh particles promote the conversion of CO 2 via dissociated H, allowing the formation of formate species at low temperature. The formate species and the hydride rhodium complexes are considered reaction intermediates.[a] Prof.

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