Dimethyl ether (DME) is a versatile raw material and an interesting alternative fuel that can be produced by the catalytic direct hydrogenation of CO2. Recently, this process has attracted the attention of the industry due to the environmental benefits of CO2 elimination from the atmosphere and its lower operating costs with respect to the classical, two-step synthesis of DME from syngas (CO + H2). However, due to kinetics and thermodynamic limits, the direct use of CO2 as raw material for DME production requires the development of more effective catalysts. In this context, the objective of this review is to present the latest progress achieved in the synthesis of bifunctional/hybrid catalytic systems for the CO2-to-DME process. For catalyst design, this process is challenging because it should combine metal and acid functionalities in the same catalyst, in a correct ratio and with controlled interaction. The metal catalyst is needed for the activation and transformation of the stable CO2 molecules into methanol, whereas the acid catalyst is needed to dehydrate the methanol into DME. Recent developments in the catalyst design have been discussed and analyzed in this review, presenting the different strategies employed for the preparation of novel bifunctional catalysts (physical/mechanical mixing) and hybrid catalysts (co-precipitation, impregnation, etc.) with improved efficiency toward DME formation. Finally, an outline of future prospects for the research and development of efficient bi-functional/hybrid catalytic systems will be presented.
We studied different preparation methods to synthesize a series of bifunctional hybrid catalytic systems for the direct synthesis of DME from syngas. The objective was to optimize the contact and interaction between the methanol synthesis catalyst and the methanol dehydration catalyst (Cu/ZnO/Al 2 O 3 and H 3 PW 12 O 40 supported on TiO 2 , respectively) by using different mixing methods (simple mixing, mixing−milling, suspension, and mixing−pressing). It has been found that the close contact between methanol synthesis and acidic functions is highly dependent on the degree of mixing of the two catalysts. In this respect, the hybrid catalyst prepared by mixing−pressing, which represents the closest contact, shows the strongest alterations in both catalytic functions. These modifications are associated with a decrease in copper surface area and a decrease in strong acid sites caused by the physical blocking of active sites or by cation exchange of the Cu 2+ /Zn 2+ species from Cu−ZnO(Al) and the H + from the H 3 PW 12 O 40 units. The activity results demonstrated that the mixing−pressing method leading to a closer contact between the two catalytic functions led to a very low dimethyl ether time yield compared to the other bifunctional catalysts prepared by less severe mixing methods (19.4 vs 205−335 μmol/min•g cat ). This work clearly indicates the importance of the mixing method in the synthesis of the hybrid catalyst to optimize the distance and interaction between the metal and acid sites.
Tabasco is located in one of the ten more important basins of North America. One third of all water resources in Mexico passes through here. Flooding events are part of the natural history of the basin; however floods have increased spatially and in magnitude. Data regarding total annual rainfalls as high as 4000 mm are registered regularly within the border of Tabasco and Chiapas. The most important wetlands of Mexico are located here on the low river basin of the Grijalva and Usumacinta rivers. Since ancient times, people in this part of Mexico are related to this flooding system in a variety of ways. A system of dams generates most of the electricity power used on Southern Mexico. Oil exploitation, cattle breeding and agriculture are the main economic activities and are responsible for an important loss of the natural ecosystems and ecosystem services. The objective of this research was to study flooding causes in this area. Geomorphology, climate, topography, hydrology and soil maps were constructed. A historical review of floods, river courses, and land use as well as an analysis of meteorological data were performed. Ecosystem vulnerability was evaluated. Results show that there has been a loss of 90% of the original biodiversity of tropical forest due mainly to farming and poor cattle management activities. Road infrastructure, unplanned urban growth and oil exploitation infrastructure has caused an important impact especially on the hydrodynamics and coastal areas. Extraordinary events with more than 200 mm in 24 hours are more common each year. The amount and intensity of floods today has increased and put at risk a great number of the population. Climate change : would increase the possibility of floods. Results propose conservation policies to protect or recover ecosystem services.
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