70 research outputs found
Photoelectrochemical reactors for CO2 utilization
The photoelectrochemical reduction of CO2 to renewable fuels and valuable chemicals using solar energy is a research topic that has attracted great attention recently due to its potential to provide value-added products under the Sun, solving the issues related to global warming at the same time. This review covers the main research efforts made on the photoelectrochemical reduction of CO2. Particularly, the study focuses in the configuration of the applied reactor, which is a topic scarcely explored in the literature. This includes the main materials used as photoelectrodes and their configuration in the photoelectrochemical reactor, which are discussed for technical uses. The review provides an overview of the state-of-the-art processes and aims to help in the development of enhanced photoelectroreactors for an efficient CO2 utilization.The authors acknowledge the financial support from the Spanish Ministry of Economy and Competitiveness (MINECO) under the project CTQ2016-76231-C2-1-R and RamonÌ y Cajal programme (RYC-2015-17080)
Interfacial Chemistry in the Electrocatalytic Hydrogenation of CO_{2} over C-Supported Cu-Based Systems
Operando soft and hard X-ray spectroscopic techniques were used in combination with plane-wave density functional theory (DFT) simulations to rationalize the enhanced activities of Zn-containing Cu nanostructured electrocatalysts in the electrocatalytic CO2 hydrogenation reaction. We show that at a potential for CO2 hydrogenation, Zn is alloyed with Cu in the bulk of the nanoparticles with no metallic Zn segregated; at the interface, low reducible Cu(I)-O species are consumed. Additional spectroscopic features are observed, which are identified as various surface Cu(I) ligated species; these respond to the potential, revealing characteristic interfacial dynamics. Similar behavior was observed for the Fe-Cu system in its active state, confirming the general validity of this mechanism; however, the performance of this system deteriorates after successive applied cathodic potentials, as the hydrogen evolution reaction then becomes the main reaction pathway. In contrast to an active system, Cu(I)-O is now consumed at cathodic potentials and not reversibly reformed when the voltage is allowed to equilibrate at the open-circuit voltage; rather, only the oxidation to Cu(II) is observed. We show that the Cu-Zn system represents the optimal active ensembles with stabilized Cu(I)-O; DFT simulations rationalize this observation by indicating that Cu-Zn-O neighboring atoms are able to activate CO2, whereas Cu-Cu sites provide the supply of H atoms for the hydrogenation reaction. Our results demonstrate an electronic effect exerted by the heterometal, which depends on its intimate distribution within the Cu phase and confirms the general validity of these mechanistic insights for future electrocatalyst design strategies
Interfacial chemistry in the electrocatalytic hydrogenation of CO2 over C-Supported Cu-Based systems
Operando soft and hard X-ray spectroscopic techniques were used in combination with plane-wave density functional theory (DFT) simulations to rationalize the enhanced activities of Zn-containing Cu nanostructured electrocatalysts in the electrocatalytic CO2 hydrogenation reaction. We show that at a potential for CO2 hydrogenation, Zn is alloyed with Cu in the bulk of the nanoparticles with no metallic Zn segregated; at the interface, low reducible Cu(I)âO species are consumed. Additional spectroscopic features are observed, which are identified as various surface Cu(I) ligated species; these respond to the potential, revealing characteristic interfacial dynamics. Similar behavior was observed for the FeâCu system in its active state, confirming the general validity of this mechanism; however, the performance of this system deteriorates after successive applied cathodic potentials, as the hydrogen evolution reaction then becomes the main reaction pathway. In contrast to an active system, Cu(I)âO is now consumed at cathodic potentials and not reversibly reformed when the voltage is allowed to equilibrate at the open-circuit voltage; rather, only the oxidation to Cu(II) is observed. We show that the CuâZn system represents the optimal active ensembles with stabilized Cu(I)âO; DFT simulations rationalize this observation by indicating that CuâZnâO neighboring atoms are able to activate CO2, whereas CuâCu sites provide the supply of H atoms for the hydrogenation reaction. Our results demonstrate an electronic effect exerted by the heterometal, which depends on its intimate distribution within the Cu phase and confirms the general validity of these mechanistic insights for future electrocatalyst design strategies
On choosing the most appropriate catalysts for the conversion of carbon dioxide to fuels and other commodities, and on the environmentally benign processing of renewable and nonrenewable feedstocks
Synthesis of TiO2 Thin Films: Relationship Between Preparation Conditions and Nanostructure
CO2 capture and reduction to liquid fuels in a novel electrochemical setup by using metal-doped conjugated microporous polymers
An Integrated Approach for the Early Detection of Runaway Reactions by Using UV-Visible and Temperature Sensors
A new approach for the early runaway detection in chemical reactors by coupling UV-visible and temperature
sensors was developed. Measurable variables such as i) conversion and ii) temperature were used as input to
our model based on the divergence calculation. The runaway criterion was defined when the divergence of the
reactor becomes positive on a segment of the reaction path.
We used a lab-scale chemical reactor (0.5 L) working under batch isoperibolic conditions, equipped with two
kinds of sensors: i) a set of three Pt thermo-resistances for measuring the temperatures both within the reactor
and in the cooling jacket and ii) an UV-visible probe for the indirect evaluation of the conversion through
measurements of light absorbance.
The early warning detection system (EWDS) was tested for the sulphuric acid catalyzed esterification of acetic
anhydride and methanol, a very simple reaction but releasing ~ 70 kJ per mole of anhydride consumed. The
responses given by EWDS were examined during the simulation of runaway reactions Different chemical heat
flows were generated by varying the concentration of the sulphuric acid and adding at once the acetic
anhydride into the reactor. The behaviour of the detection criterion was evaluated comparing the EWDS
signals using both temperature and conversion as input variables, with the responses obtained from only
temperature measurements. A detailed kinetic model was also developed to solve the differential energy and
mass balance equations and define the runaway boundaries.
Results showed the importance of an input variable indirectly related to conversion in such kinds of processes
where other enthalpy variations (i.e. due to an endothermic mixing of the reagents) may hide a thermal
runaway
Reaction inhibition as a method for preventing thermal runaway in industrial processes
In this work inhibitors were used to prevent runaway reactions during
methylmethacrylate suspension polymerization processes. The main problem that
may more frequently occur in chemical reactors, carrying out free radical polymerization
reactions, is the loss of temperature control. The addition of an inhibitor
during polymerization processes can be considered as a good method to stop or at
the least slow down the reaction. In this work two inhibitors were used: hydroquinone
and 1,4-benzoquinone in a series of polymerization experiments. In order to identify
situations that can lead to a runaway reaction, an early warning detection system
based on the divergence criterion was used. When this system signalled an alarm,
small amounts of inhibitor were added to the reaction mixture. The results showed
that hydroquinone and 1,4-benzoquinone behave slightly differently and the reactor
temperature can be kept within safe limits
AN INTEGRATED APPROACH FOR THE EARLY DETECTION OF RUNAWAY REACTIONS BY USING UV-VISIBLE AND TEMPERATURE SENSORS
We report here on a novel approach for the early runaway detection in chemical reactors, based on the integration of two kinds of sensors: i) a set of three Pt thermo-resistances for measuring the temperatures both within the reactor and in the cooling jacket and ii) an UV-visible probe for the indirect evaluation of the conversion through measurements of light absorbance. The measured variables (temperature and conversion) were used as input to our model based on the divergence calculation. The early warning detection system (EWDS) was tested for the sulphuric acid catalyzed esterification of acetic anhydride and methanol, a very simple reaction but releasing ~70 kJ per mole of anhydride consumed. The responses given by EWDS were examined during the simulation of runaway reactions in a lab-scale reactor working under batch isoperibolic conditions. Different chemical heat flows were generated by varying the concentration of the sulphuric acid and adding at once the acetic anhydride into the reactor. The behaviour of the detection criterion was evaluated comparing the EWDS signals using both temperature and conversion as input variables, with the responses obtained from only temperature measurements. A detailed kinetic model was also developed to solve the differential energy and mass balance equations and define the runaway boundaries. Results showed the importance of an input variable indirectly related to conversion in such kinds of processes where other enthalpy variations (i.e. due to an endothermic mixing of the reagents) may hide a runaway reaction occurring
- âŠ