Final Report Summary - ADMIENV (Advanced Electron Microscopy techniques applied to catalytic materials for energy generation with very low environmental impact)
The aim of the project ADMIENV (234418) was to make a productive contribution in two different approaches: (1) the implementation in the University of Cadis of the electron tomography technique and (2) the design at a nanometric scale of heterogeneous catalysts for CO oxidation reactions. Catalysts to study are constituted by a high atomic number support (cerium-zirconium mixed oxide) and the active metallic phase consist of Au and Ru, proven the good activity of these metals for CO oxidation.
Electron tomography technique is now available and fully operative at the University of Cadis. Data sets were acquired in the JEOL 2010 FEG microscope of the Central Services of Science and Technology of the University of C?dis, tilting in a wide range of rotation through the use of a Fischione Tomography specimen holder model 2030 acquired for this purpose. The data set is aligned and reconstructed using FEI Inspect 3D software and the final result is visualised using the program Amira. The use of the Electron Tomography Technique, not available in many research centers today, allows to establish numerous collaborations with other research institutions, both national and foreign, which is translated into an increase in the number and quality of scientific publications.
Regarding the preparation of the catalysts, a cerium-zirconium mixed oxide with composition Ce0. 6Zr0. 4O2 provided by Grace Davison was used as support in order to compare the results with previous studies performed in our laboratory. This support is subjected to a reduction-oxidation treatment (so called SRMO) to improve the redox properties of the system.
The gold metallic phase was prepared by the deposition-precipitation method. This term is often used in the preparation of catalysts with gold, but in the strict sense refers to a process by which a basic solution is deposited on the carrier surface in order to gradually increase the pH of the solution in which the support is suspended. When done properly the entire active phase is added to the support. In our work method for catalyst preparation a solution Na2CO3 is used as basic agent to maintain the preparation environment at a pH around 8.
To obtain catalysts with an active phase consisting of the two metals (gold and ruthenium) supported on cerium and zirconium oxide treated by SRMO, 3 different synthetic routes were used:
I. Gold deposition-precipitation, followed by impregnation Ruthenium
This synthetic route is based on two stages. During the first one, gold is deposited using the deposition-precipitation method described previously and a second stage of impregnation of ruthenium using the incipient wetness impregnation method followed by a reduction at 350 °C.
II. Impregnation of ruthenium, followed by gold deposition-precipitation.
This synthetic route is also based on two steps, first preparing the ruthenium catalyst by impregnation as explained previously. This route allowed the elimination of nitrates with a thermal treatment before carrying out the step of gold deposition-precipitation, thus avoiding subjecting the gold to the severe heat treatment which may produce the formation of big aggregates. The second stage of gold deposition-precipitation is carried out as explained before for monometallic gold catalyst.
III. Deposition-precipitation of both metals at the same time.
This route of preparation of the bimetallic catalysts is similar to that explained for preparing supported gold catalysts, but in this case both metals are deposited simultaneously using a solution of both metal precursors (HAuCl4 and RuCl3). The drying of the sample is performed at 100° C for 12 hours in a muffle oven. The obtained sample is divided into two parts, one is subjected to an oxidation treatment at 250° C and the other part is reduced at 250 °C
The prepared catalysts were studied by electron microscopy in HAADF-STEM mode to characterise the particle size and metallic dispersion in order to select the most appropriate preparation method. HAADF-STEM images show an intensity proportional to the square of the atomic number, Z, so the metallic particles can be distinguished easily from the support. Using this methodology, the method of preparation with which smaller particles are obtained proved to be the first one, gold deposition-precipitation followed by impregnation of ruthenium. The series of catalysts prepared using this method have been studied in depth, using both microscopes at Cadis University and other institutions (CEA Grenoble and University of Antwerp) to analyze with the highest possible resolution the composition of the metal particles by means of XEDS, resulting that only-ruthenium nanoparticles have a narrow size-distribution (1-2 nm), only-gold nanoparticles have a size distribution between 2-6 nm, and some bimetallic nanparticles have been found with intermediate particle sizes around 3-5 nm. In terms of catalytic activity for CO oxidation, the bimetallic catalysts have proved to be very active, behave in a very similar manner to those of ruthenium alone in terms of their performance and stability against aggregation.
Thus, a good understanding of the problem has been achieved, what may help for new design strategies for bimetallic catalysts devoted to CO oxidation.
Out of this grant, a new research line has been partially implemented. A doctoral fellow has been recruited for 4 month, a student was recruited for 5 months and when he got a fellowship to finish his PhD a female student was recruited for 7 months and also got additional funding for finishing her PhD. Finally, for the last period of the project, a doctoral fellow was recruited part time (16 hours per week) during 8 months. The scientific results related with the project have been gathered in 14 peer-reviewed papers and four more that are in progress. The scientific results have been presented in international conferences as 9 oral communications and 4 posters.
Electron tomography technique is now available and fully operative at the University of Cadis. Data sets were acquired in the JEOL 2010 FEG microscope of the Central Services of Science and Technology of the University of C?dis, tilting in a wide range of rotation through the use of a Fischione Tomography specimen holder model 2030 acquired for this purpose. The data set is aligned and reconstructed using FEI Inspect 3D software and the final result is visualised using the program Amira. The use of the Electron Tomography Technique, not available in many research centers today, allows to establish numerous collaborations with other research institutions, both national and foreign, which is translated into an increase in the number and quality of scientific publications.
Regarding the preparation of the catalysts, a cerium-zirconium mixed oxide with composition Ce0. 6Zr0. 4O2 provided by Grace Davison was used as support in order to compare the results with previous studies performed in our laboratory. This support is subjected to a reduction-oxidation treatment (so called SRMO) to improve the redox properties of the system.
The gold metallic phase was prepared by the deposition-precipitation method. This term is often used in the preparation of catalysts with gold, but in the strict sense refers to a process by which a basic solution is deposited on the carrier surface in order to gradually increase the pH of the solution in which the support is suspended. When done properly the entire active phase is added to the support. In our work method for catalyst preparation a solution Na2CO3 is used as basic agent to maintain the preparation environment at a pH around 8.
To obtain catalysts with an active phase consisting of the two metals (gold and ruthenium) supported on cerium and zirconium oxide treated by SRMO, 3 different synthetic routes were used:
I. Gold deposition-precipitation, followed by impregnation Ruthenium
This synthetic route is based on two stages. During the first one, gold is deposited using the deposition-precipitation method described previously and a second stage of impregnation of ruthenium using the incipient wetness impregnation method followed by a reduction at 350 °C.
II. Impregnation of ruthenium, followed by gold deposition-precipitation.
This synthetic route is also based on two steps, first preparing the ruthenium catalyst by impregnation as explained previously. This route allowed the elimination of nitrates with a thermal treatment before carrying out the step of gold deposition-precipitation, thus avoiding subjecting the gold to the severe heat treatment which may produce the formation of big aggregates. The second stage of gold deposition-precipitation is carried out as explained before for monometallic gold catalyst.
III. Deposition-precipitation of both metals at the same time.
This route of preparation of the bimetallic catalysts is similar to that explained for preparing supported gold catalysts, but in this case both metals are deposited simultaneously using a solution of both metal precursors (HAuCl4 and RuCl3). The drying of the sample is performed at 100° C for 12 hours in a muffle oven. The obtained sample is divided into two parts, one is subjected to an oxidation treatment at 250° C and the other part is reduced at 250 °C
The prepared catalysts were studied by electron microscopy in HAADF-STEM mode to characterise the particle size and metallic dispersion in order to select the most appropriate preparation method. HAADF-STEM images show an intensity proportional to the square of the atomic number, Z, so the metallic particles can be distinguished easily from the support. Using this methodology, the method of preparation with which smaller particles are obtained proved to be the first one, gold deposition-precipitation followed by impregnation of ruthenium. The series of catalysts prepared using this method have been studied in depth, using both microscopes at Cadis University and other institutions (CEA Grenoble and University of Antwerp) to analyze with the highest possible resolution the composition of the metal particles by means of XEDS, resulting that only-ruthenium nanoparticles have a narrow size-distribution (1-2 nm), only-gold nanoparticles have a size distribution between 2-6 nm, and some bimetallic nanparticles have been found with intermediate particle sizes around 3-5 nm. In terms of catalytic activity for CO oxidation, the bimetallic catalysts have proved to be very active, behave in a very similar manner to those of ruthenium alone in terms of their performance and stability against aggregation.
Thus, a good understanding of the problem has been achieved, what may help for new design strategies for bimetallic catalysts devoted to CO oxidation.
Out of this grant, a new research line has been partially implemented. A doctoral fellow has been recruited for 4 month, a student was recruited for 5 months and when he got a fellowship to finish his PhD a female student was recruited for 7 months and also got additional funding for finishing her PhD. Finally, for the last period of the project, a doctoral fellow was recruited part time (16 hours per week) during 8 months. The scientific results related with the project have been gathered in 14 peer-reviewed papers and four more that are in progress. The scientific results have been presented in international conferences as 9 oral communications and 4 posters.