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Papers by Dante Chiavassa

Reliability Data Collection and Use in Risk and Availability Assessment, 1986

The information collected from equipments operating in industrial plants for a reliability data b... more The information collected from equipments operating in industrial plants for a reliability data bank (RDB) has peculiarities that make difficult its posterior statistical treatment. Its vaguenesses and indeterminations could not be obviate and must be analyzed.

Studies in Surface Science and Catalysis, 1993

Abstract The activity (TOF) and selectivity for methanol and methane syntheses from CO/H 2 using ... more Abstract The activity (TOF) and selectivity for methanol and methane syntheses from CO/H 2 using Pd supported onto structurally different silicas (macro and microporous, DAVISON G-59 and G-03 types, resp.) has been evaluated. Reaction tests followed a careful follow-up of each of the preparation steps leading to the final catalysts. CH 3 OH is the main product on Pd/G-59 but with Pd/G-03 methane selectivity is much higher. In general the TOF CH 3 OH decreases smoothly, but TOF CH 4 shows a marked descent, by increasing the exposed metal fraction (FE) of Pd.

Chemical Engineering Journal, 2015

h i g h l i g h t s A novel Carberry-type well-mixed catalytic microreactor is presented. Both ba... more h i g h l i g h t s A novel Carberry-type well-mixed catalytic microreactor is presented. Both batch (transient) or continuous operation is feasible. Carefully controlled temperature and pressure (up to 3 MPa) conditions achievable. Continuous measurement of gas phase composition by mass spectrometry is provided. The device performance was validated by comparing measured reaction rates with literature data.

Journal of Catalysis, 2012

The effect of palladium-gallia interaction in Pd(1 wt.%)/b-Ga 2 O 3 during selective methanol syn... more The effect of palladium-gallia interaction in Pd(1 wt.%)/b-Ga 2 O 3 during selective methanol synthesis by CO 2 hydrogenation was studied. A detailed quasi-in situ transmission electron microscopy analysis of the as-prepared H 2-reduced catalyst, without exposing it to air, showed that Ga-Pd bimetallic (nano)particles were formed under a reductive atmosphere at or above 523 K. However, these particles were unstable; upon air exposure, a dramatic and extensive encapsulation of the metallic crystallites by Ga 2 O 3 occurred. In addition, the function of the bimetallic particles in the mechanism of methanol synthesis was investigated by in situ infrared spectroscopy at 0.7 MPa. The results confirmed those of previous studies in which the stepwise hydrogenation of (bi)carbonate to formate and then to methoxy groups on the Ga 2 O 3 surface took place via a bifunctional pathway. In this pathway, the role of the Ga-Pd bimetallic crystallites was to provide atomic hydrogen, via spillover, to the oxidic surface and to hamper both CH 3 OH decomposition and CO production.

Catalysis Today, 2013

ABSTRACT The synthesis of methanol via catalytic hydrogenation of carbon oxides was evaluated in ... more ABSTRACT The synthesis of methanol via catalytic hydrogenation of carbon oxides was evaluated in two groups of Cu–Ga2O3–ZrO2 ternary catalysts containing 2 wt%.Cu. Copper was incorporated in the first group either by incipient wetness (IW) or by ion exchange (IE), both on the pure oxides (Ga2O3 and ZrO2) and the x-Ga2O3/ZrO2 mixed oxides (where x = 1, 6 or 9 wt% Ga2O3). In a second group of materials galia was incorporated onto Cu/ZrO2 previously dried or dried/calcined. The catalytic evaluations were performed in a tubular microreactor at 3 MPa, 523 K, GHSV = 20,000 h−1 using two different gas mixtures. The first mixture contained CO2 and CO (M1: H2/CO2/CO = 75/22/3), while in the second one carbon monoxide was replaced by He (M2: H2/CO2/He = 75/22/3).The yield to methanol was progressively higher with gallia loading, but the best catalyst tested had an intermediate loading of Ga2O3 deposited onto a dried and calcined Cu/ZrO2 precursor which was obtained, in turn, by ion exchanging copper nitrate to the zirconia. The catalysts for which gallium were added to the dried and calcined IE Cu/ZrO2 precursor were the most stable.

Catalysis Today, 2011

The production of methanol via the catalytic hydrogenation of carbon oxides was simulated in a re... more The production of methanol via the catalytic hydrogenation of carbon oxides was simulated in a reacting system that included the recycling of noncondensable gases (H 2 , CO 2 and CO) to evaluate the CO 2 capture capability of the process. As a first step, the asymptotic responses of the system 'operating in thermodynamic equilibrium' (i.e., overall recoveries of CO 2 and H 2 , CH 3 OH selectivity and productivity) were analyzed for various industrial conditions of pressure (3-5 MPa), temperature (508-538 K), feed composition (H 2 /CO 2 = 1.5/1 to 4/1) and mole recycle ratio (R) with respect to the molar feed flow rate. Then the performance of two catalysts (a novel one, Pd-Ga 2 O 3 /SiO 2 and a commercial CuO/ZnO/Al 2 O 3 type) in an ideal isothermal, isobaric, pseudohomogeneous fixed-bed reactor was studied for a broad range of W/F CO 2 ratios. It was found that, whereas the 'reactor in equilibrium' would allow up to 100% CO 2 capture, the capture values upon using these catalysts were significantly lower. Nevertheless, such recoveries always increased whenever R was raised, which implies that catalyst development efforts in this field should prioritize achievement of the highest catalytic activity (i.e., specific productivity) rather than attempt catalyst selectivity improvements.

Catalysis Today, 2008

The synthesis of methanol from CO 2 /H 2 on a Ga 2 O 3-Pd/silica catalyst, together with the reve... more The synthesis of methanol from CO 2 /H 2 on a Ga 2 O 3-Pd/silica catalyst, together with the reverse water gas shift reaction, was modeled for a wide range of temperatures (508-538 K), pressures (1-4 MPa), compositions (H 2 /CO 2 = 1, 3 and 6) and space velocity conditions. The kinetic information was combined with relevant spectroscopic (FT-IR) data. The rate determining steps (rds) of the reactions were the hydrogenation of the formate intermediate, and its decomposition on the gallia surface, respectively. A competitive adsorption mechanism, where adsorbed atomic hydrogen occupies the same active sites as other oxygenated surface intermediates on the gallia, was found as the most satisfactory, in terms of physicochemical significance of the parameter estimates. Minimal residuals were found when considering as kinetically relevant the simultaneous surface occupancy by formate, methylenebisoxy, hydroxyl and atomic hydrogen intermediates. The deleterious impact of CO for certain process conditions, such as high conversion and/or ternary H 2 /CO 2 /CO mixture feeds, was also studied. In these cases, CO competes with H 2 on the Pd crystallites, severely limiting the availability of atomic hydrogen to the gallia surface. Using the steady-state approximation, the supply and demand of atomic hydrogen were then balanced to find the best model interpretation of the observed reactivity.

Catalysis Letters, 2005

The hydrogenation of CO 2 was investigated on Ga 2 O 3-promoted Pd/SiO 2 catalyts and mechanical ... more The hydrogenation of CO 2 was investigated on Ga 2 O 3-promoted Pd/SiO 2 catalyts and mechanical mixtures of Ga 2 O 3 /SiO 2 and Pd/SiO 2 catalysts (H 2 /CO 2 =3; P=3.0 MPa; T=523 K). By means of the latter it was possible to demonstrate that atomic hydrogen, H s , can be generated by Pd 0 far from Ga 2 O 3 , and move (spill-over) there to reach the other reactive species (formates) and complete the reaction cycle. The reaction results indicate that (as also evidenced by in situ FTIR) the Ga 2 O 3-Pd/SiO 2 catalyst works as a true bi-functional system. The metal-promoter intimacy is not decisive in terms of the catalytic chemistry of the system, but the closeness between the Pd crystallites and the Ga 2 O 3 surface patches boost the activity, owing to a minimized effort in the H s supply to the latter.

Journal of CO2 Utilization

Abstract The performance of two copper-based catalysts, Cu/ZrO2 and Ga2O3/Cu/ZrO2, in regards the... more Abstract The performance of two copper-based catalysts, Cu/ZrO2 and Ga2O3/Cu/ZrO2, in regards the reverse water gas shift (RWGS) reaction as compared with their reaction rates for the methanol synthesis reaction (RCH3OH) was studied using H2/CO2 mixtures at 1.6 and 0.1 MPa, at 498 K. The reactivity studies were carried out using a Carberry-type microcatalytic reactor operated in the batch (transient) mode after H2 prereduction at 523 K (2 h). Measurements of the catalytic activity were also made using D2/CO2 mixtures (0.1 MPa, 498 K) to assess isotope effects. For Cu/ZrO2, the initial RWGS reaction rate using D2 instead of H2 was slightly higher whereas such rate was about equal for the ternary catalyst. Kinetic rate expressions obtained from the Langmuir-Hinshelwood-Hougen-Watson formalism were used to model and analyze the experimental results and the reaction mechanism(s) of the RWGS on these catalysts. Congruence was found between the experimental results and a reaction mechanism where (predominantly) CO2 adsorbs dissociatively on the Cu particles (rate-determining step). The reduction of (ad)oxygen and surface hydroxyls follow afterwards.

Studies in Surface Science and Catalysis, 1998