New publication in Angewandte Chemie

New work on the role of the oxide support in stabilising and activating Pd nanoparticle catalysts, published in Angewandte. Driven by the experimental work of our colleagues in Bayreuth and supported by Dianwei.

Abstract:

Ultrathin layers of oxides deposited on atomically flat metal surfaces have been shown to significantly influence the electronic structure of the underlying metal, which in turn alters the catalytic performance. Upscaling of the specifically designed architectures as required for technical utilization of the effect has yet not been achieved.

Here, we apply liquid crystalline phases of fluorohectorite nanosheets to fabricate such architectures in bulk. Synthetic sodium fluorohectorite, a layered silicate, when immersed into water spontaneously and repulsively swells to produce nematic suspensions of individual negatively charged nanosheets separated to more than 60 nm, while retaining parallel orientation. Into these galleries oppositely charged palladium nanoparticles were intercalated whereupon the galleries collapse. Individual and separated Pd nanoparticles were thus captured and sandwiched between nanosheets. As suggested by the model systems, the resulting catalyst performed better in the oxidation of carbon monoxide than the same Pd nanoparticles supported on external surfaces of hectorite or on a conventional Al2O3 support. XPS confirmed a shift of Pd 3d electrons to higher energies upon coverage of Pd nanoparticles with nanosheets to which we attribute the improved catalytic performance. DFT calculations showed increasing positive charge on Pd weakened CO adsorption and this way damped CO poisoning.

Dean’s Award

Congratulations to Tereza Benesova, for winning the Dean’s award for best bachelor thesis in chemistry and physics of special materials, for her work “Theoretical investigation of the interaction of water with zeolites at high temperatures“!

Fine work, and thoroughly deserved!

New publication in ACS Catalysis

Dianwei’s recent work, investigating the structures and migration pathways of ultrasmall Pt clusters in zeolites has been published in ACS Catalysis. Congratulations on a nice bit of work, which changes the common perception of zeolites as largely inert surfaces for metal clusters.

Abstract:

The mechanism by which single metal atoms and small, zeolite-encapsulated metal particles are stabilized against migration and growth is not currently well understood. In this work, we employ an unbiased density functional global optimization strategy to identify the locations and energetic barriers for migration pathways between sites for platinum (Pt) confined within the microporous volume of a purely silicious zeolite with Linde type A topology and its aluminosilicate and borosilicate variants.

We observe an impressive stabilization of single Pt atoms caused by a hitherto unreported binding mode, in which the six rings in the framework are broken, leading to trapped, highly accessible metal centers. In addition, heteroatom substituents are found to significantly enhance the incorporation of Pt via an unexpected insertion into framework SiO–H bonds. Migration of Pt is hindered by high barriers, which are predicted to vary significantly with Si:X (X = Al and B) ratios. I

t is proposed that an optimal Si:X ratio exists for a given zeolite topology, in which the barriers will reach the maximum value. The energetic preference for Pt clustering (via Ostwald ripening) remains but is significantly reduced with respect to isolated clusters because of the strong interactions between Pt atoms and the framework.

Our findings suggest a means to control noble-metal particle sintering, despite a thermodynamic driving force toward Pt clustering. This work provides an explanation for the surprisingly high degree of kinetic stability of ultrasmall, encapsulated metal particles observed experiment.

New grant underway:

New three-year GACR grant beginning: “Stability of Metal Particles Encapsulated in Zeolites: Multiscale Modelling and Experimental Benchmarking.”

Abstract:

Sub-nanometre noble metal particles are highly efficient catalysts for a range of industrially important reactions. Such systems have enormous potential, but are limited by their inherent instability with respect to sintering. A popular method to reduce sintering while retaining accessibility is encapsulation into a zeolite matrix. However, the mechanism of sintering inside zeolites is poorly understood, and the redispersal mechanism under pressure of gases, which is crucial for catalyst recycling, is also lacking.

In this project we aim to develop a realistic and predictive model of particle migration, growth and redispersal for zeolite-encapsulated noble metal elements. This will be achieved by a combination of state-of-the-art computational methods (density functional global optimization, ab-initio molecular dynamics and microkinetic modelling), and experimental synthesis and characterisation (HRTEM) of encapsulated metal particles.

Looking forward to getting started, and teaming up with our experimental collaborators!

Water in Zeolites Meeting - Liblice

Several of us attended the Workshop at Liblice Castle in the Czech Republic entitled “Water in Zeolites”, with oral presentations from Mengting, Mingxiu and CJH, and poster presentations from Tereza and Indranil:

-”Theoretical Study of Zeolite Hydrolysis under Alkaline Conditions” -M. Jin

-”The influence of defects on zeolite hydrolysis barriers” - M. Liu

-”Operando modelling of Germanosilicate hydrolysis” - CJH

-”Theoretical study of zeolite-water interactions under streaming conditions” -T. Benesova

-”Understanding Germanosilicate Hydrolytic (In)stability based on Germanium Distributions derived using Neural Network Potentials” -I. Saha