Designing new catalysts: synthesis of new active structures: general discussion

Abstract

opened the discussion of the introductory lecture by Avelino Corma: The metal nanoparticles inside the zeolites are in a different environment from those outside. Is there any difference in their chemistry and their catalytic behaviour?Avelino Corma answered: We were not able to determine the differences in reactivity, other than the accessibility of reactants with different sizes. It should be said that we did not use molecules specically suited for showing potential electronic-entropic differences. I agree that this is an important point to be considered. What we clearly observed is that the clusters inside the channels were stable towards sintering.Cynthia Friend asked: Have you considered the possible effect of ligands bound to your clusters? Have van der Waals' interactions been explicitly included?Avelino Corma replied: The theoretical calculation of the interactions of nitrobenzene with the nanoparticles includes the interactions with the support and van der Waals' interactions. In the case of clusters, H 2 dissociation has been carried out on isolated Pt, Au and Au-Pt clusters and van der Waals' interactions were not considered.Graham Hutchings continued: You rightly point out in your design strategy that the adsorption of the reactant is the key factor, and that adsorption occurs This journal is preferentially via the nitro group when reacting substituted nitrobenzenes. What happens if you add an additional nitro group? Will this inevitably lead to oligomers being formed?Avelino Corma responded: If the molecule has two nitro groups to be reduced, instead of one, it is not a problem.On the contrary, for the coupling of the corresponding amino groups derived from nitrobenzene to form the azo compounds, we did not see the formation of trimers or tetramers.The consecutive steps are slow and the higher molecular weight products would be difficult to desorb at the lower reaction temperatures.Bruce Gates remarked: A valuable goal with metal cluster catalysts is to control the cluster nuclearity. With a zeolite as a support, the clusters may be stabilized. What confers that stability? Is it a connement effect associated with the structure of the zeolite? Are there other issues at play? Avelino Corma answered: Indeed I believe that besides a connement effect, which should be more important in small pore zeolites, the zeolite framework with the electric elds associated and interactions with the framework oxygen atoms can also stabilize charged metal clusters.Parasuraman Selvam asked: Where do you draw a line to distinguish between the clusters and nanoparticles in terms of the size and shape? Are these clusters amorphous or crystalline? What do we understand about these aspects in terms of their activity towards a chosen reaction?In general, the driving force for the adsorption is the coordinative unsaturation of the active sites. In this context, the nanoclusters/nanoparticles have denite sizes and shapes, viz., the corners, edges and faces, and predominantly the sites at the faces are utilized for the react...

Operando Surface Studies on Metal-Oxide Interfaces of Bimetal and Mixed Catalysts

“…187 The segregated oxygen-containing TM components, such as CoO x and NiO x , and its oxide species of CoO and NiO unaffectedly cover the topmost layer of Pt-skin/Pt-TM structure. Thus, the oxygendriven emerging species take part in the reaction pathway with other adsorbate molecules during industrial reactions that the defect or redox-mediated metastable morphology is also considered the active site 188 for the unprecedented tuning of catalytic activity in previous literature of operando analysis for efficient energy-conversion systems. 189−191 One representative example of the Pt-TM oxide structure is partially oxidized FeO 1−x clusters on the Pt(111) surface; the observed morphology by STM in UHV shows peculiar triangular-shaped nanoislands of FeO monolayer in Figure 8c.…”

An efficient microwave-assisted chelation (MWAC) post-synthetic modification method to produce hierarchical Y zeolites

“…For example, faujasite (FAU) type Y zeolites are the most important material in petroleum refinery catalysts for fluid catalytic cracking (FCC) and hydrocracking [4], being estimated to account for a share of 61.1% of the total market of synthetic zeolites in 2018, regarding value [2]. The intrinsic micropores of these zeolites (<1 nm) lead to the long standing challenge of limitation on accessibility and diffusion during catalysis [5], for example, the reduced accessibility of active sites within the pore structure to the reactants and the slow diffusion rate of the products from the pores to the bulk media. The * Corresponding author.…”

Cellulose nanocrystals (CNCs) as hard templates for preparing mesoporous zeolite Y assemblies with high catalytic activity

“…Y zeolite is crystalline, microporous ( pore width = 0.74 nm) and rigid, offering good mechanical and hydrothermal stability under the severe con-ditions used in FCC processes (>500°C). 3,4 Diffusion limitation imposed by intrinsic micropores of zeolites is one of the major causes of low activity and/or deactivation in zeolite catalysis, 5 especially for reactions involving molecules larger than 1 nm. 6,7 Therefore, enormous effort has been spent on overcoming the diffusion limitation and enhancing the accessibility of the active surface within the framework zeolites, leading to the development of the state-of-the-art zeolitic materials such as nanozeolites, [8][9][10] zeolitised mesoporous materials, and zeolites with mesoporosity (or the so-called mesoporous zeolites).…”