Jorge E. Sambeth

Recovery of manganese oxides from spent alkaline and zinc-carbon batteries. An application as catalysts for VOCs elimination.

Manganese, in the form of oxide, was recovered from spent alkaline and zinc-carbon batteries employing a biohydrometallurgy process, using a pilot plant consisting in: an air-lift bioreactor (containing an acid-reducing medium produced by an Acidithiobacillus thiooxidans bacteria immobilized on elemental sulfur); a leaching reactor (were battery powder is mixed with the acid-reducing medium) and a recovery reactor. Two different manganese oxides were recovered from the leachate liquor: one of them by electrolysis (EMO) and the other by a chemical precipitation with KMnO4 solution (CMO). The non-leached solid residue was also studied (RMO). The solids were compared with a MnOx synthesized in our laboratory. The characterization by XRD, FTIR and XPS reveal the presence of Mn2O3 in the EMO and the CMO samples, together with some Mn(4+) cations. In the solid not extracted by acidic leaching (RMO) the main phase detected was Mn3O4. The catalytic performance of the oxides was studied in the complete oxidation of ethanol and heptane. Complete conversion of ethanol occurs at 200°C, while heptane requires more than 400°C. The CMO has the highest oxide selectivity to CO2. The results show that manganese oxides obtained using spent alkaline and zinc-carbon batteries as raw materials, have an interesting performance as catalysts for elimination of VOCs.

Catalytic oxidation of CH3OH to HCOOCH3 on V2O5 : A theoretical study

Abstract In a previous work, the CH 3 OH adsorption-oxidation process on V 2 O 5 was studied by mass spectrometry analysis of the reaction atmosphere. The following partial oxidation products were reported: H 2 CO, CO, CO 2 , (CH 3 O) 2 CH 2 (methylal), CH 3 OCH 2 OH (hemimethylal) and HCOOCH 3 . The data so obtained allowed a reaction pathway to be proposed. In the present work, we used models of the plane (010) of V 2 O 5 and of CH 3 OH, to test whether the pathway proposed in this work as well as alternative ones presented by other authors were energetically favorable or not. With this purpose, the variation of the total system energy was computed in each step by extended Huckel-type calculations (ASED, atom superposition and electron delocalization). The results showed, on the one hand, that the pathway proposed in this work is better than alternatives pathways, and on the other hand, the possible existence of other equally-favorable adsorption sites in which bridge oxygen may take part.

A theoretical-experimental study of Wells-Dawson acid: An explanation of their catalytic activity

Abstract A theoretical–experimental study about the behaviour of the protons and their interactions with water molecules on the Wells–Dawson acid and their influence on the catalytic activity was done. The Wells–Dawson acid (H6P2W18O62·nH2O) was characterised by TGA analysis. Besides, DRIFTS and 1 H MAS-NMR measurements as a function of acid treatment temperature were done. These experimental results, consistent with prior studies, suggest that the protonic acidity is related to the presence of water molecules in the heteropolyoxoanion (HPA) structure. In particular, the H5O2+ species associated with the last two H2O molecules determined by TGA analysis and the 1 H MAS-NMR measurements show that the presence of H5O2+ species plays an important role in the acidity–catalytic activity relationship. The Wells–Dawson acid structure formation was studied by calculating the relative energy of the system. The possible acid molecular structure (P2W18O62H6·nH2O) was analysed considering different steps by associating to the Wells–Dawson anion (P2W18O62)−6, the protons, water molecules and secondary structures. The theoretical calculus by extended Huckel method (EHMO) was done analysing the most energetically favourable positions for the protons. The theoretical results indicate that three different water species associated to the Wells–Dawson acid structure can exist. Besides, these results show that the H5O2+ species are the most energetically stable ones in the acid structure. These species bonds two secondary structures of Wells–Dawson acid leading to minimum system energy. It can be expected that these species are the last water molecules lost in the acid structure at the end of acid dehydration process. This assumption is in agreement with the results obtained with the three experimental techniques previously mentioned.

Exposure and risk analysis to particulate matter, metals, and polycyclic aromatic hydrocarbon at different workplaces in Argentina

In order to estimate air quality at work environments from small and medium-sized enterprises (SMEs), we determined both the concentration of particulate matter (PM10 and PM2.5) and the presence of polycyclic aromatic hydrocarbons (PAHs), as the heavy metals in the composition of the particulate matter. Three SMEs located in the city of La Plata, Argentina, were selected: an electromechanical repair and car painting center (ERCP), a sewing work room (SWR), and a chemical analysis laboratory (CAL). The results evidenced high levels of PM exceeding the limits allowed by the USEPA and the presence of benzo(k)fluoranthene in all the analyzed sites and benzo(a)pyrene in the most contaminated site (ERCP). Regarding metals, the presence of Cd, Ni, Cu, Pb, and Mn, mainly in the fraction of PM2.5, in the same workplace was found. As far as risk assessment at all the workplaces surveyed is concerned, risk values for contracting cancer throughout life for exposed workers (LCR) did not comply with the parameters either of USEPA or of WHO (World Health Organization).

Catalytic and physicochemical characterization of the MnVOx system. Influence of vanadium on methanol oxidation

Manganese and mixed vanadium oxides were prepared by the hydrolysis of acetylacetonates. They were characterized by different techniques, such as X-ray diffraction, XPS, temperature-programmed surface reaction (TPSR), and conversion and selectivity measurements. TPSR studies showed that H2O, CO2, and O2 are present in manganese oxide samples and that the ones containing vanadium desorb CO2, H2O, methanol, formaldehyde, O2. The vanadium-free catalysts and the ones with a lower vanadium content also exhibit high methanol conversion and selectivity to CO2 at higher temperatures. The selectivity to dimethyl ether is important in the catalyst without V at lower temperature. The greatest conversion at lower temperatures and the highest selectivities to CO2 are achieved with the catalysts having the highest vanadium content.

Adsorption of CH3OH on V2O5: Comparative reactivity of the (100) and (010) planes

Abstract Methanol adsorption on the (100) and (010) planes of V 2 O 5 was analysed by Extended Huckel Method (ASED). For the plane (100) two cases were considered with vanadium atoms either saturated or unsaturated with oxygen atoms. The results showed that CH 3 OH adsorption on the (010) plane is more favourable than on the (100) plane for both cases.