Operando Modelling of Al-NMR published (Chem. Sci.)

New work published in Chemical Science, on the effect of dynamics, solvation, temperature and zeolite structure on the simulation of ss-NMR isotropic chemical shifts.

ClusterMeeting 2023

This year we brought several people to the cluster meeting in Prague. Postdoc Andreas Erlebach, PhD student Tereza Benesova, bachelor students Kristyna Pokorna and Jakub Szmitek and myself were present. We had one talk, four posters and a session chair, so the group was well represented.

I gave a talk which aimed to cover the work of everyone (in 15 minutes!), entitled “Accelerated modelling of supported Pt clusters via reactive machine learning potentials“.

As ever, it was great to meet colleagues past and present, and come up with new ideas for future work and collaborations. It’s always a highlight of the conference year.

CIS-9 conference

Tereza and I visited Toledo for the Czech-Italian-Spanish meeting on catalysis and molecular sieves.

I gave a talk on cluster-zeolite and cluster-surface interactions, based on the recent work of Tereza and Jakub.

Tereza gave her first conference presentation - on the mechanisms of oxygen exchange in zeolites interrogated with water under steaming conditions. Very well presented!

Tereza’s Talk in Toledo

Before the chaired session

Octahedral Aluminium-published (Angewandte)

Abstract:

While the structures of Brønsted acid sites (BAS) in zeolites are well understood, those of Lewis acid sites (LAS) remain an active area of investigation. Under hydrated conditions, the reversible formation of framework-associated octahedral aluminum has been observed in zeolites in the acidic form. However, the structure and formation mechanisms are currently unknown. In this work, combined experimental 27Al NMR spectroscopy and computational data reveal for the first time the details of the zeolite framework-associated octahedral aluminium. The octahedral LAS site becomes kinetically allowed and thermodynamically stable under wet conditions in the presence of multiple nearby BAS sites. The critical condition for the existence of such octahedral LAS appears to be the availability of three protons: at lower proton concentration, either by increasing the Si/Al or by ion-exchange to non-acidic form, the tetrahedral BAS becomes thermodynamically more stable. This work resolves the question about the nature and reversibility of framework-associated octahedral aluminium in zeolites

Very sad news. Over the Christmas break we lost an excellent scientist, a great group leader, an inspirational teacher and a good man in Petr Nachtigall. His fine work, keen eye for an interesting problem and clear enthusiasm for understanding how things really work were the reasons I came to Prague in the first place. He was an inspiration for how to behave with fairness, integrity and honesty, and always had the best interests of his group, his students and his department at heart. His legacy will be not just his impressive scientific output, but how to conduct onesself in the world of science. He was a far-sighted person, who sought to make things better.

He will be missed by us all.

https://www.natur.cuni.cz/fakulta/aktuality/zemrel-profesor-petr-nachtigall-1

New work published in Angewandte Chemie

Abstract:

Supported metal nanoparticles are used as heterogeneous catalysts but often deactivated due to sintering at high temperatures. Confining metal species into a porous matrix reduces sintering, yet supports rarely provide additional stabilization. Here, we used the silanol-rich layered zeolite IPC-1P to stabilize ultrasmall Rh nanoparticles. By adjusting the IPC-1P interlayer space through swelling, we prepared various architectures, including microporous and disordered mesoporous. In situ scanning transmission electron microscopy confirmed that Rh nanoparticles are resistant to sintering at high temperature (750 °C, 6 hrs). Rh clusters strongly bind to surface silanol quadruplets at IPC-1P layers by hydrogen transfer to clusters, while high silanol density hinders their migration based on density functional theory calculations. Ultimately, combining swelling with long-chain surfactant and utilizing metal-silanol interactions resulted in a novel, catalytically active material—Rh@IPC_C22.

PhD defence x2!

Congratulations to (Dr) Dianwei Hou and (Dr) Mengting Jin, for successfully defending their PhD theses in a friday viva double header.

It’s been 5 years, 6 papers and many conferences. I’m pleased that they have navigated the process, and best of luck to Mengting in her new teaching position in China, and to Dianwei for his Postdoc plans in Korea!

Thanks also to Andrew Logsdail and Mira Rubes for attending as opponents.

congrats to both !

Masters Monday

Congratulations to Tereza for passing the Masters defence with the highest grade!

Looking forward to starting the PhD STARS project on stabilising metal clusters for single atom catalysis!

Telluride Energy Landscapes Meeting

I was able to attend the Energy Landscapes Meeting in an (experimental) hybrid mode this year.

This is one of my favourite meetings, with a completely free-form schedule, no-limits talks and endless discussion. Fascinating topics, ranging from modelling COVID response statistics, to enzymatic nanomachines, all within the broad scope of energy landscapes and thermodynamics.

It was my third visit, and the first in a virtual format. Real shame not to make it out to Colorado, but despite the time difference, it worked pretty well. I hope 2 hours of Pt cluster diffusion wasn’t too much for the other attendees! Thanks especially to Christian Schoen for inviting me. I hope to be back in person soon.

IZC 2022 contributions

We had a good turnout at the IZC meeting in Valencia, where Indranil, Deborah and Martin Kubu presented posters on:

“Understanding Germanosilicate Hydrolytic (in)stability Based on Germanium Distributions Derived using Neural Network Potentials ”,

“Experimental and Theoretical 17O NMR for Characterisation of Siliceous Zeolites”

“The Role of Water Loading and Germanium Content in Germanosilicate Hydrolysis”.

I was given a talk entitled:

“Insights into the Dynamics of Zeolite-Encapsulated Pt Clusters via Machine Learning”,

while Petr also presented:

“Operando Modeling of Zeolites: Time-Averaged 27Al NMR Tensors based on Double-Machine Learning Approach”

IZC website

Deborah, me and Indranil at the end of 5 1/2 days of zeolites!

SFB TACO visit

Thanks for Gareth Parkinson for inviting me to present our recent work in reactive machine learning for modelling zeolite materials at the TACO seminar series at TU Wien. It was my first time visiting this institute and city, and great conversations and vegan pizza were enjoyed!

TACO SFB link

Cluster Surface Interaction meeting 2022

I was lucky enough to reconnect with the cluster community at the cluster surface interactions meeting in Genoa. This was originally planned for April 2020, and I intended to go to meet the people in the field, some of whom I haven’t seen in 10 years, at the start of the GAČR project. In the end it became a chance to report what we’ve done in the 2.5 years so far!

I gave a talk entitled “Insights into Cluster-Zeolite Dynamics from Kinetic Modelling and Machine Learning”.

Link to the Meeting Website

New work published in RSC Catal. Sci. Tech.

Abstract:

The encapsulation of noble metal atoms into zeolites is a promising route to generate controlled size distributions of stable metal catalysts. Pinning of single metal atoms to particular binding sites represents the optimal atom-efficiency and is a desirous outcome, despite the propensity of metal clusters to sinter. Currently, sintering resistance of noble metals in siliceous and high-silica frameworks is incompletely understood, while the role of influencing factors such as adsorbates and metal element identity, have not been ascertained.

Here, we investigate the nature of metal–zeolite interactions, via density functional global structure optimisation and kinetic Monte Carlo simulations of the binding and migration of Pt and Au in a siliceous zeolite with framework topology LTA. We show that strong binding of Pt atoms to the framework severely hinders migration, even in the absence of framework heteroatoms, while Au diffuses freely through the pore. Reducing agents CO and H2 change the preferred binding site of Pt and flatten the potential energy surface, which reduces migration barriers and thereby promotes particle growth. PtCO is found to represent a compromise between strongly framework-bound Pt1, and bulky, volatile Pt(CO)x clusters, exhibiting fast diffusion.

This work provides an atomistic picture of single metal atom kinetics inside high-silica zeolites, which represent a fundamental basis for understanding nano-catalyst deactivation.

New work published in ACS Chemistry of Materials

Abstract:

The controlled desilication of zeolites, leading to hierarchical micro-/mesoporous materials, is one of the most promising approaches to increase the application potential of zeolites. It can lift the restrictions connected to diffusion limitations in many industrially important processes and it can also modify the Si/Al ratio of the final material. The selective desilication of zeolites is generally performed under alkaline conditions, and control over the degree of framework degradation is maintained via the Si:Al ratio of the parent sample and the pH of the solution. However, the mechanism of alkaline hydrolysis in zeolites is poorly understood at present: the role of microsolvation of ions and the role of micropore confinement effects are currently unknown.

In this work, we establish the mechanisms for the alkaline hydrolysis of siliceous zeolite chabazite (CHA) occurring from within the pore. Energetically facile reaction pathways are identified, which directly involve NaOH and confirm that NaOH may not only play a role as a reactant but also as a catalyst. We demonstrate that collective effects play a decisive role in the mechanism: initiation of the reaction via formation of Q3 defects becomes spontaneous when the Na+ cation is solvated by a sufficient amount of water and subsequent barriers along the desilication pathway are lowered. We show that it is crucial to include a realistic treatment of the hydration environment to capture the processes, which occur inside zeolite pores.

This work advances our understanding of a ubiquitous process in heterogeneous catalysts and will help in controlled desilication treatments for zeolite upgrading.

New publication in Advanced Materials

New review paper in advanced materials - Zeolite-water interactions is a fascinating and rich area of study, with crucial industrial importance. Here we summarize the current understanding, based on the significant insights gained in recent years, both experimentally and via computational research.

Abstract:

Zeolites are among the most environmentally friendly materials produced industrially at the Megaton scale. They find numerous commercial applications, particularly in catalysis, adsorption, and separation. Under ambient conditions aluminosilicate zeolites are stable when exposed to water or water vapor. However, at extreme conditions as high temperature, high water vapor pressure or increased acidity/basicity, their crystalline framework can be destroyed. The stability of the zeolite framework under aqueous conditions also depends on the concentration and character of heteroatoms (other than Al) and the topology of the zeolite.

The factors critical for zeolite (in)stability in the presence of water under various conditions are reviewed from the experimental as well as computational sides. Nonreactive and reactive interactions of water with zeolites are addressed. The goal of this review is to provide a comparative overview of all-silica zeolites, aluminosilicates and zeolites with other heteroatoms (Ti, Sn, and Ge) when contacted with water. Due attention is also devoted to the situation when partial zeolite hydrolysis is used beneficially, such as the formation of hierarchical zeolites, synthesis of new zeolites or fine-tuning catalytic or adsorption characteristics of zeolites.

New work published in ACS Journal of Physical Chemistry C.

Abstract:

The Assembly–Disassembly–Organization–Reassembly (ADOR) process has been used extensively to prepare new zeolite frameworks based on germanosilicate precursors. The disassembly step exploits the lability of the bonds in the presence of water to selectively disconnect the framework, prior to reorganization into new framework topologies. However, a mechanistic understanding of this crucial step is lacking: specifically, the roles of heteroatom (germanium) content and water loading in zeolite hydrolytic instability.

In this work, ab initio free energy simulations, coupled with water vapor adsorption measurements reveal that collectivity effects control the reactivity of the archetypal ADORable zeolite UTL toward water. A transition between reversible and irreversible water adsorption occurs as water loading is increased, leading to reactive transformations. Clustering of germanium is observed to activate hitherto unreported favorable hydrolysis mechanisms beyond a threshold concentration of three atoms per double four ring unit, demonstrating that the heteroatom distribution and collectivity in the hydrolysis mechanism can drastically influence zeolite framework instability.

These findings suggest that control over heteroatom content, distribution, and hydration level is important to achieve the controlled partial hydrolysis of zeolitic frameworks and is likely to apply not only to other ADORable germanosilicate zeolites but also to Lewis acidic zeolites in general.

Czech-Italian-Spanish Young Researchers Conference 2021

I was honoured to be invited to give a plenary talk at the youngresearchers CIS 2021 conference, which was held online from 6-8 September this year. So I decided to go with my favourite topic - modelling ultrasmall metal clusters: “Understanding Supported Sub-Nanometre Metal Clusters: A Perspective from Theory“.

Hopefully it was useful, and if not, at least interesting!

Contributions to clustermeeting 2021

From July 18-23, we were fortunate enough to have our first in-person meeting for quite some time, at the cluster meeting, held in Prague, and organized by Stefan Vajda, Alessandro Fortunelli and Armin Kleibert.

I was given a “hot topic” talk, entitled “Stabilization, Migration and Sintering of Zeolite-Encapsulated Metal Clusters“, and Dianwei delivered a poster on his recent work in the same area.

Disordered Initial State

But eventually a crystalline solid

clustercake 2021

FEZA 2021

Several talks at FEZA 2021 (hosted by the BZA in Brighton, UK) but held online.

I presented “Operando Modelling of Zeolite Hydrolysis: Solvation, Defects and pH Effects“, which combined the recent work of Mingxiu and Mengting, while Andreas presented the recent developments in reactive neural network potentials for silicate-based materials.

Shame not to get to visit the seaside, but a great conference nonetheless, with a diverse range of talks.

IMN 2021: Leuven

International meeting on Nanoalloys, organised in Leuven by Ewald Janssens and colleagues, held online.

I was able to present a poster entitled “Dynamical Properties of Zeolite-Encapsulated Sub-Nanometre Metal Particles“, based on recent global optimization, kinetic modelling and machine learning work of Andreas, Lukas and Dianwei.

Presenting a poster online via pdf is an odd experience, but worked surprisingly well with breakout rooms. Thanks Leuven for making the best of the situation!