A new generation of Titanium based catalysts for ethylene polymerization has been developed through the Surface Organometallic Chemistry (SOMC) methodology using a novel type of silica support having a 3D fibrous morphology, KCC-1. The first type of Tibased catalyst was obtained by reacting isolated silanol surface groups, ≡SiOH of KCC-1 (dehydroxylated at 700 ⁰C under high vacuum, 10-5 bar) with titanium (IV) tetraneopentyl, Ti(CH2tBu)4 to produce [(≡SiO)Ti(CH2tBu)3]. The second type of Ti-based catalyst was generated by using an Al-modified KCC-1. The peculiarity of this support is due to the presence of tetra-coordinated aluminum-bound hydroxyl group, [(≡Si-O-Si≡)(≡SiO)2Al- OH] that can be used as a Lewis Acid anchor sites and generate new catalytic properties. The well-defined [(≡Si-O-Si≡)(≡SiO)2Al-OH] was obtained by reacting diisopropylaluminum hydride with KCC treated at 700 °C followed by a thermal treatment at 400 °C and oxidation with N2O. IR spectra of pyridine adsorbed on the Al sites show that these were strong Lewis acid sites (constituting 80% of the total Al sites). Thus, the highly electrophilic support surface was used to create a single well-defined surface organo-titanium fragment [(≡Si–O–Si≡)(≡Si–O–)2Al–O–Ti(CH2tBu)3] by the reaction of the surface [(≡Si–O–Si≡)(≡Si–O)2Al–OH]) groups with Ti(CH2-tBu)4 at room temperature for 4 h in dry pentane. The performance of each Ti-supported catalyst assessed for ethylene polymerization. It was found that Al-modified support (highly electrophilic) provide better activity compared to the unmodified one. Indeed, the productivity of the catalyst [(≡Si–O– Si≡)(≡Si–O–)2Al–O–Ti(CH2tBu)3] was found to be 67.8 g of PE/ 1mmol Ti/ 1h with molecular weight of 3208408 g/mol; polydispersity was found to be 2.3, and (HDPE) high-density polyethylene was obtained. In contrast, [(≡SiO)Ti(CH2tBu)3] (unmodified one) produces lower molecular weight polymer 989843 g/mol, higher polydispersity (PD) 6.7 and low-density polyethylene (LDPE) productivity was found to be 14.670 g PE/1mmol Ti /1h. These results demonstrate that modification of the oxide ligands on silica through a generation of Al Lewis acid site opens up new catalytic properties, markedly enhancing the catalytic performance of supported organotitanium species. We also demonstrate how the silica mesostructure (2D vs 3D ) affects the catalytic activity in ethylene polymerization. While SBA15 (2D) could limit the accessibility of the active sites resulting in lower yield. In contrast, KCC-1 (3D) are more active in ethylene polymerization, because the active sites reside on the external surface are fully accessible to the substrate.

No description available.

The major goals of this work were to: develop a new methodology for the preparation of site-isolated catalytic sites on a silica surface, prepare the first truly single-site supported metallocene/CGC polymerization catalyst, and develop structure-reactivity relationships for these new systems. To synthesize these novel catalysts, the approach taken was to develop a protocol which allows for the synthesis of an aminosilica material with isolated, uniform amine sites. This patterned aminosilica was then used as a scaffold to support a constrained geometry catalyst. These functionalizations occurred at essentially a quantitative level, in stark contrast to previous literature reports. The patterned catalysts were evaluated in the polymerization of ethylene and compared to densely loaded literature materials. Overall, it was found the patterned materials were 5-10 times more active than traditional immobilized CGC catalysts. The patterned catalysts were also found to be effective catalysts for the copolymerization of norbornenes (including functionalized norbornenes) and ethylene, the first reported use of a tethered CGC for the production of ethylene-norbornene copolymers. The control materials were inactive in these polymerizations, providing further evidence that the patterning protocol allows for the synthesis of unique highly active, isolated catalytic sites. Various structural components of the immobilized CGC developed in this work were tested for their impact on catalyst synthesis and reactivity in ethylene polymerizations. The results showed the patterned materials in general behaved according to the trends seen in homogeneous CGC polymerizations. These results, while congruent with similar homogeneous CGC studies, are in direct conflict with previous work on supported CGCs reported in the literature. This discrepancy is likely the result of the difference between the isolated, possibly single-site patterned catalysts developed in the course of this work and the multi-sited catalysts prepared by traditional supporting protocols. This also further illustrates the difficulty in developing structure-reactivity relationships when ill-defined solid catalysts are used.

The general objective of this thesis is the analysis of selective reactions for group VI grafted metal complexes via methods and principles of SOMC. For this objective, three approaches have been chosen. The first chapter is an introduction to the topic of selectivity in catalysis, emphasizing heterogeneous catalysis and more specifically the different approaches to support catalysts on surfaces. The concept of catalysis by design is introduced as a new way to use the surface as a ligand. Chapter 2 presents the results of a library of well-defined catalysts of group VI with identical catalytic functionality, but different ligand environment. The results reveal, that metal-carbynes are able to switch their catalytic reactivity based on the substrate that they are contacted with. The difference in reaction mechanisms and the differing reactivities towards the substrates are presented. It can be concluded that the classical ROMP is selectively achieved with cyclic alkene substrates leading to polymers whereas cyclic alkanes yield exclusively higher and lower homologues of the substrate without polymeric products. Chapter 3 presents the study of olefin metathesis of cis-2-pentene with metal-carbynes of group VI, where the selectivity of the catalyst library towards yield of cis-/trans products is analyzed. It is presented, that the ligand environment of the catalysts is showing an influence in the selectivity. Rates of cis/trans isomerization of the products are high and are approaching thermodynamic equilibrium at high conversion. Product isomerization, thermodynamic equilibrium and reactivity differences between liquid phase and gas phase products are analyzed. Chapter 4 presents the full characterization of tungsten-hydrides by selective transformation into tungsten-hydroxides. These newly discovered well-defined tungstenhydroxides are fully characterized by ICP, TEM, DRIFT, double quantum and triple quantum solid-state NMR. The presented results allow to predict that tungsten-hydrides on KCC-1700 are present as two distinct species. Catalysis results with cyclooctane show, that due to burial of the complexes in the KCC-1700 surface the tungsten-hydrides are less active towards cyclic alkane metathesis reactions with bulky cyclooctane than the metalcarbyne complexes. Chapter 5 is giving a conclusion of results and an outlook for catalytic applications of the generated tungsten-hydroxides of chapter 4.

No description available.

O criptorquidismo é a uma afecção hereditária caracterizada por ausência de um ou ambos os testículos na bolsa escrotal devido à interrupção de seu trajeto normal de migração da cavidade abdominal para a bolsa escrotal. Tal interrupção faz com que o testículo se apresente ectópico, permanecendo no tecido subcutâneo, abdômen ou região do anel inguinal. Para a correção desta patologia, indica-se, na Medicina Veterinária, a criptorquidectomia convencional ou laparoscópica, sendo que a laparoscópica tem se firmado como melhor alternativa devido ao menor trauma tecidual, melhor visualização, menor dor, necessidade de menor analgesia, tempo menor de recuperação do paciente e melhor aspecto do ferimento cirúrgico. Este estudo objetivou desenvolver uma técnica para criptorquidectomia através de um único portal (LESS-single site surgery) utilizando o trocarte Centry Port®, com apenas dois canais de trabalho. Foram utilizados dez coelhos machos, da raça Nova Zelândia e Califórnia, com peso entre 2,8 kg e 3,85 kg. Após a intubação e manutenção do plano anestésico e colocação do animal em posição de Trendelenburg a 200, foi introduzido o Centry Port® aproximadamente a 1 cm cranial à cicatriz umbilical através de incisão de aproximadamente 1,5 cm de extensão. O pneumoperitôneo com CO2 foi estabelecido e mantido durante todos os procedimentos com 10 mm Hg. Por meio de compressão manual o testículo foi introduzido para o interior da cavidade abdominal através do anel inguinal. Após sua visualização e apreensão com uma pinça de Kelly, foi fixado à parede abdominal com auxílio de sutura transparietal. A hemostasia foi realizada com auxílio da eletrocoagulação bipolar regulada em 20 watts. Após a secção do cordão espermático os testículos foram removidos por dentro do trocarte. Ao término dos procedimentos laparoscópicos e após a inspeção da cavidade, foi desfeito o pneumoperitôneo, sendo realizada a sutura da musculatura e da pele. Todos os tempos cirúrgicos foram anotados, para que uma curva de aprendizado fosse avaliada. As intercorrências cirúrgicas não foram clinicamente significativas e o procedimento foi factível em todos os animais do experimento. Os coelhos foram doados após a retirada dos pontos. As maiores dificuldades encontradas com o uso do Centry Port® foram a visualização em linha e o choque entre as mãos do cirurgião e câmera junto ao trocarte. Concluiu-se com este estudo que a técnica de criptorquidectomia por single-port em coelhos, utilizando o Centry Port® é viável e que as dificuldades são superadas na medida em que a equipe estabelece maior experiência com a técnica por um único acesso. / The cryptorchidism is a hereditary disease characterized by the absence of one or both testicles in the scrotum due to interruption of their normal migration path of the abdominal cavity to the scrotum. Such interruption causes the testicle is ectopic, remaining in the subcutaneous tissue, abdomen or inguinal ring region. In Veterinary Medicine, the indication for this is the exerese surgical pathology by means of conventional or laparoscopic criptorquidectomia and laparoscopic has signed as a better alternative due to the less tissue trauma, better view, less pain, less need for analgesia, less patient recovery time and better aspect of the surgical wound. This study aimed to develop a technique to criptorquidectomia through a single portal (LESSsingle site surgery) using the Centry Port® trocar, with only two working channels. Ten male rabbits were used, the New Zealand-bred and California, weighing between 2.8 kg and 3.85 kg. After intubation and anesthetic plan maintenance and placement of the animal in the Trendelenburg position 200, Centry Port® was introduced approximately 1 cm cranial to the umbilical scar through incision about 1.5 cm long. The pneumoperitôneo with CO2 was established and maintained during all procedures with 10 mm Hg. Through manual compression the testicle was introduced into the abdominal cavity through the inguinal ring. After your viewing and seizure with a clamp on Kelly, was attached to the abdominal wall with the aid of transparietal suture. The haemostasis was performed with the aid of bipolar electrocoagulation adjusted to 20 watts. After the section of the spermatic cord the testicles were removed inside the trocar. At the end of laparoscopic procedures and after inspection of the well, was shattered the pneumoperitôneo, being performed the suture of the muscles and the dermal suture. All surgical times were noted for which a learning curve to be evaluated. The surgical complications were not clinically significant and the procedure was doable in all animals in the experiment. The rabbits were donated after the withdrawal of points. The major difficulties encountered with the use of Centry Port® were viewing online and the clash between the hands of the surgeon and the camera next to the trocar. This study concluded that the technique of criptorquidectomia by single-port in rabbits using Centry Port® is feasible and that the difficulties related to its use are exceeded in that the team establishes greater experience with the technique by single port.

O criptorquidismo é a uma afecção hereditária caracterizada por ausência de um ou ambos os testículos na bolsa escrotal devido à interrupção de seu trajeto normal de migração da cavidade abdominal para a bolsa escrotal. Tal interrupção faz com que o testículo se apresente ectópico, permanecendo no tecido subcutâneo, abdômen ou região do anel inguinal. Para a correção desta patologia, indica-se, na Medicina Veterinária, a criptorquidectomia convencional ou laparoscópica, sendo que a laparoscópica tem se firmado como melhor alternativa devido ao menor trauma tecidual, melhor visualização, menor dor, necessidade de menor analgesia, tempo menor de recuperação do paciente e melhor aspecto do ferimento cirúrgico. Este estudo objetivou desenvolver uma técnica para criptorquidectomia através de um único portal (LESS-single site surgery) utilizando o trocarte Centry Port®, com apenas dois canais de trabalho. Foram utilizados dez coelhos machos, da raça Nova Zelândia e Califórnia, com peso entre 2,8 kg e 3,85 kg. Após a intubação e manutenção do plano anestésico e colocação do animal em posição de Trendelenburg a 200, foi introduzido o Centry Port® aproximadamente a 1 cm cranial à cicatriz umbilical através de incisão de aproximadamente 1,5 cm de extensão. O pneumoperitôneo com CO2 foi estabelecido e mantido durante todos os procedimentos com 10 mm Hg. Por meio de compressão manual o testículo foi introduzido para o interior da cavidade abdominal através do anel inguinal. Após sua visualização e apreensão com uma pinça de Kelly, foi fixado à parede abdominal com auxílio de sutura transparietal. A hemostasia foi realizada com auxílio da eletrocoagulação bipolar regulada em 20 watts. Após a secção do cordão espermático os testículos foram removidos por dentro do trocarte. Ao término dos procedimentos laparoscópicos e após a inspeção da cavidade, foi desfeito o pneumoperitôneo, sendo realizada a sutura da musculatura e da pele. Todos os tempos cirúrgicos foram anotados, para que uma curva de aprendizado fosse avaliada. As intercorrências cirúrgicas não foram clinicamente significativas e o procedimento foi factível em todos os animais do experimento. Os coelhos foram doados após a retirada dos pontos. As maiores dificuldades encontradas com o uso do Centry Port® foram a visualização em linha e o choque entre as mãos do cirurgião e câmera junto ao trocarte. Concluiu-se com este estudo que a técnica de criptorquidectomia por single-port em coelhos, utilizando o Centry Port® é viável e que as dificuldades são superadas na medida em que a equipe estabelece maior experiência com a técnica por um único acesso. / The cryptorchidism is a hereditary disease characterized by the absence of one or both testicles in the scrotum due to interruption of their normal migration path of the abdominal cavity to the scrotum. Such interruption causes the testicle is ectopic, remaining in the subcutaneous tissue, abdomen or inguinal ring region. In Veterinary Medicine, the indication for this is the exerese surgical pathology by means of conventional or laparoscopic criptorquidectomia and laparoscopic has signed as a better alternative due to the less tissue trauma, better view, less pain, less need for analgesia, less patient recovery time and better aspect of the surgical wound. This study aimed to develop a technique to criptorquidectomia through a single portal (LESSsingle site surgery) using the Centry Port® trocar, with only two working channels. Ten male rabbits were used, the New Zealand-bred and California, weighing between 2.8 kg and 3.85 kg. After intubation and anesthetic plan maintenance and placement of the animal in the Trendelenburg position 200, Centry Port® was introduced approximately 1 cm cranial to the umbilical scar through incision about 1.5 cm long. The pneumoperitôneo with CO2 was established and maintained during all procedures with 10 mm Hg. Through manual compression the testicle was introduced into the abdominal cavity through the inguinal ring. After your viewing and seizure with a clamp on Kelly, was attached to the abdominal wall with the aid of transparietal suture. The haemostasis was performed with the aid of bipolar electrocoagulation adjusted to 20 watts. After the section of the spermatic cord the testicles were removed inside the trocar. At the end of laparoscopic procedures and after inspection of the well, was shattered the pneumoperitôneo, being performed the suture of the muscles and the dermal suture. All surgical times were noted for which a learning curve to be evaluated. The surgical complications were not clinically significant and the procedure was doable in all animals in the experiment. The rabbits were donated after the withdrawal of points. The major difficulties encountered with the use of Centry Port® were viewing online and the clash between the hands of the surgeon and the camera next to the trocar. This study concluded that the technique of criptorquidectomia by single-port in rabbits using Centry Port® is feasible and that the difficulties related to its use are exceeded in that the team establishes greater experience with the technique by single port.

O criptorquidismo é a uma afecção hereditária caracterizada por ausência de um ou ambos os testículos na bolsa escrotal devido à interrupção de seu trajeto normal de migração da cavidade abdominal para a bolsa escrotal. Tal interrupção faz com que o testículo se apresente ectópico, permanecendo no tecido subcutâneo, abdômen ou região do anel inguinal. Para a correção desta patologia, indica-se, na Medicina Veterinária, a criptorquidectomia convencional ou laparoscópica, sendo que a laparoscópica tem se firmado como melhor alternativa devido ao menor trauma tecidual, melhor visualização, menor dor, necessidade de menor analgesia, tempo menor de recuperação do paciente e melhor aspecto do ferimento cirúrgico. Este estudo objetivou desenvolver uma técnica para criptorquidectomia através de um único portal (LESS-single site surgery) utilizando o trocarte Centry Port®, com apenas dois canais de trabalho. Foram utilizados dez coelhos machos, da raça Nova Zelândia e Califórnia, com peso entre 2,8 kg e 3,85 kg. Após a intubação e manutenção do plano anestésico e colocação do animal em posição de Trendelenburg a 200, foi introduzido o Centry Port® aproximadamente a 1 cm cranial à cicatriz umbilical através de incisão de aproximadamente 1,5 cm de extensão. O pneumoperitôneo com CO2 foi estabelecido e mantido durante todos os procedimentos com 10 mm Hg. Por meio de compressão manual o testículo foi introduzido para o interior da cavidade abdominal através do anel inguinal. Após sua visualização e apreensão com uma pinça de Kelly, foi fixado à parede abdominal com auxílio de sutura transparietal. A hemostasia foi realizada com auxílio da eletrocoagulação bipolar regulada em 20 watts. Após a secção do cordão espermático os testículos foram removidos por dentro do trocarte. Ao término dos procedimentos laparoscópicos e após a inspeção da cavidade, foi desfeito o pneumoperitôneo, sendo realizada a sutura da musculatura e da pele. Todos os tempos cirúrgicos foram anotados, para que uma curva de aprendizado fosse avaliada. As intercorrências cirúrgicas não foram clinicamente significativas e o procedimento foi factível em todos os animais do experimento. Os coelhos foram doados após a retirada dos pontos. As maiores dificuldades encontradas com o uso do Centry Port® foram a visualização em linha e o choque entre as mãos do cirurgião e câmera junto ao trocarte. Concluiu-se com este estudo que a técnica de criptorquidectomia por single-port em coelhos, utilizando o Centry Port® é viável e que as dificuldades são superadas na medida em que a equipe estabelece maior experiência com a técnica por um único acesso. / The cryptorchidism is a hereditary disease characterized by the absence of one or both testicles in the scrotum due to interruption of their normal migration path of the abdominal cavity to the scrotum. Such interruption causes the testicle is ectopic, remaining in the subcutaneous tissue, abdomen or inguinal ring region. In Veterinary Medicine, the indication for this is the exerese surgical pathology by means of conventional or laparoscopic criptorquidectomia and laparoscopic has signed as a better alternative due to the less tissue trauma, better view, less pain, less need for analgesia, less patient recovery time and better aspect of the surgical wound. This study aimed to develop a technique to criptorquidectomia through a single portal (LESSsingle site surgery) using the Centry Port® trocar, with only two working channels. Ten male rabbits were used, the New Zealand-bred and California, weighing between 2.8 kg and 3.85 kg. After intubation and anesthetic plan maintenance and placement of the animal in the Trendelenburg position 200, Centry Port® was introduced approximately 1 cm cranial to the umbilical scar through incision about 1.5 cm long. The pneumoperitôneo with CO2 was established and maintained during all procedures with 10 mm Hg. Through manual compression the testicle was introduced into the abdominal cavity through the inguinal ring. After your viewing and seizure with a clamp on Kelly, was attached to the abdominal wall with the aid of transparietal suture. The haemostasis was performed with the aid of bipolar electrocoagulation adjusted to 20 watts. After the section of the spermatic cord the testicles were removed inside the trocar. At the end of laparoscopic procedures and after inspection of the well, was shattered the pneumoperitôneo, being performed the suture of the muscles and the dermal suture. All surgical times were noted for which a learning curve to be evaluated. The surgical complications were not clinically significant and the procedure was doable in all animals in the experiment. The rabbits were donated after the withdrawal of points. The major difficulties encountered with the use of Centry Port® were viewing online and the clash between the hands of the surgeon and the camera next to the trocar. This study concluded that the technique of criptorquidectomia by single-port in rabbits using Centry Port® is feasible and that the difficulties related to its use are exceeded in that the team establishes greater experience with the technique by single port.

Malgré les propriétés remarquables de polyéthylène de masse molaire très élevée(UHMWPE), une généralisation de son application est limitée en raison des difficultésrencontrées lors de sa mise en forme, liées au taux d’enchevêtrement important deschaînes.Le but de ce travail est de développer des nanocomposites et des mélanges à base depolyéthylène, par polymérisation in situ. A cet effet, des catalyseurs métallocènes et despost-métallocènes ont été immobilisés par différentes méthodes sur la silice mésoporeuseSBA-15. Le système poreux de ce support, avec des canaux bien définis à l'échellenanométrique, peut entraîner des effets de confinement des chaînes macromoléculaireset/ou permettre un mélange intime des polymères.Le comportement de la polymérisation de l'éthylène par catalyses homogène et supporté,ainsi que les méthodes d'immobilisation utilisées et leur effet sur l'activité depolymérisation et des masses molaires, ont été évalués.Une caractérisation complète des nanocomposites et des mélanges comprenant différentsaspects des matériaux (morphologie, cristallinité et homogénéité) a été réalisée. Lespropriétés thermiques et mécaniques des matériaux finaux ont été également évaluées.D'une manière générale, les nanocomposites à base de polyéthylène et les mélanges enréacteur ont montré des propriétés mécaniques améliorées, en termes de moduled'élasticité, résistance mécanique, ténacité et résistance au fluage, par comparaison avec lespolyéthylènes communs. En traitant la poudre d'UHMWPE par moulage, par compression àhaute pression et au-dessous de sa température de fusion, une augmentation remarquabledes paramètres mécaniques a été obtenue.Les résultats préliminaires sur la préparation de nanocomposites en utilisant desnanocristaux de cellulose ont montré que cette approche est faisable et qu’elle présente unpotentiel de développement. / Despite the remarkable properties of ultra-high molecular weight polyethylene, itsapplication is limited by the difficulties encountered in conventional melt processing duethe high degree of entanglement of the chains.The aim of this work is to develop polyethylene based nanocomposites and in-reactorblends, by in situ polymerization. For this purpose metallocenes and post-metallocenecatalysts were immobilized by different methods on mesoporous silica SBA-15. The poroussystem of this support, with well-defined channels at the nanometric scale, may causeconfinement effects of macromolecular chains and/or potentiate intimate mixing ofpolymer blends.Ethylene polymerization behavior of the homogeneous and the supported systems alongwith the immobilization methodologies used and their effect on the polymerization activityand polymer molar masses were evaluated.A complete characterization of the nanocomposites and blends comprising different aspectsof the materials properties (morphology, crystallinity and homogeneity) was carried out.The thermal and mechanical properties of the final materials were also evaluated.In a general way the polyethylene based nanocomposites and in-reactor blends showedimproved mechanical properties, in terms of elastic modulus, mechanical strength,toughness and creep resistance, when compared with neat polyethylenes. By processing theUHMWPE powders by compression molding, at high pressure and below its meltingtemperature a remarkable increase of the mechanical parameters was obtained.Preliminary results on the preparation of nanocomposites using cellulose nanowhiskershave shown that this approach is feasible and show potential for further development.

<p>In recent decades, alternatives to traditional coal and fossil fuels were utilized to reduce carbon emissions. Among these alternatives, natural gas is a cleaner fuel and is abundant globally. Shale gas, a form of natural gas that also contains light alkanes (C2-C4), is presently being employed to produce olefins, which can be upgraded to higher molecular weight hydrocarbons. This thesis describes efforts to develop new catalytic materials and characterizations for the conversion of shale gas to fuels.</p> <p>In the first half, silica supported Pt-Cr alloys containing varying compositions of Pt and Pt₃Cr were used for propane dehydrogenation at 550°C. Although a change in selective performance was observed on catalysts with varying promoter compositions, the average nano-particle structures determined by <i>in situ</i>, synchrotron x-ray absorption spectroscopy (XAS) and x-ray diffraction (XRD) were identical. Further, this work presents a method for the characterization of the catalytic surface by these methods to understand its relationship with olefin selectivity. From this, we can gain an atomically precise control of new alloys compositions with tunable surface structures.</p> <p>Once formed by dehydrogenation, the intermediate olefins are converted to fuel-range hydrocarbons. In the second half, previously unknown single site, main group Zn²⁺ and Ga³⁺ catalysts are shown to be effective for oligomerization and the resulting products follow a Schutlz Flory distribution. Mechanistic studies suggest these catalysts form metal hydride and metal alkyl reaction intermediates and are active for olefin insertion and b-H elimination elementary steps, typical for the homogeneous, Cossee-Arlman oligomerization mechanism. Evidence of metal hydride and metal alkyl species were observed by XAS, Fourier transform infrared spectroscopy (FTIR), and H₂/D₂ isotope exchange. Understanding the reaction intermediates and elementary steps is critical for identifying novel oligomerization catalysts with tunable product selectivity for targeted applications. </p> <p> Through controlled synthesis and atomic level <i>in situ </i>characterizations, new catalysts compositions can be developed with high control over the resulting performance. An atomically precise control of the catalyst structure and understanding how it evolves under reaction conditions can help shed light on the fundamental principles required for rational catalyst design. </p>