From surface science to catalysis: lab-scale vacuum deposited catalyst production

Griffin, Ross ORCID: 0000-0002-9785-9713 (2020). From surface science to catalysis: lab-scale vacuum deposited catalyst production. University of Birmingham. Ph.D.

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Abstract

This thesis outlines the adaptation of surface techniques to nanoparticle catalyst production. The work covers the scale up of the Matrix Assembly Cluster Source (MACS), the design and development of new apparatus, dubbed the Clean Catalyst Source (CCS) and the eﬀectiveness of catalysts produced by these systems. All samples are characterised using atomic resolution Scanning Transmission Electron Microscopy (STEM). Produced catalysts are compared to those produced by Incipient Wetness Impregnation (IWI) as a model chemical synthesis method where appropriate to highlight the diﬀerences between in-vacuum and conventional solvent based production methods.

MACS produced Gold and palladium clusters are deposited onto alumina and silica powders using the MACS producing ∼1g of catalyst. Produced samples are tested for their activity in the oxidation of carbon monoxide, the reduction of 4-nitrophenol to 4-aminophenol in the presence of sodium borohydride, and the selective hydrogenation of 1-pentyne to 1-pentene as desired. All samples demonstrate activity for these reactions with the exception of gold for hydrogenation. MACS samples demonstrate similar activities to impregnated analogues at far lower loadings with cluster beam samples demonstrating high (95%) selectivity to the production of 1-pentene. Samples deposited using the MACS without matrix formation i.e; atomic rather than cluster deposition demonstrate similar structures and indistinguishable catalytic behaviour.

As a result of this similar behaviour, a new apparatus was developed and its design; based on direct sputtering of metals onto oxide powders is presented. The system uses a 10mA, 600V ion source to sputter a 150x150mm metal foil target onto a piezo ﬂuidised bed of support particles. These are tipped between covered hoppers to ensure even coating over multiple depositions. 3g of support is coated in 5 minutes, producing ∼1.1±0.4nm metal clusters by surface agglomeration. Binary palladium copper particles are produced by sequential deposition and found to be alloyed with a metallic ratio standard deviation of 0.2. This value can be halved by co-sputtering of compound (as opposed to alloyed) targets, but is not pursued due to the decreased ﬂexibility of such systems. Samples are tested for their activity in the oxidation of carbon monoxide and the selective hydrogenation of 1-pentyne. CCS samples demonstrate similar light oﬀ temperatures and selectivities for these reactions when compared with MACS samples indicating that the in vacuum or solvent free formation is dictating catalyst behaviour, as opposed to the cluster formation. Addition of copper to palladium samples results in a small decrease in selectivity contrary to expectations. Minor diﬀerences in catalytic behaviour were seen in ∼20% Cu binary particles across other test reactions.

Finally a molybdenum sublayer is used as a surface modiﬁer to produce molybdenum nucleated, molybdenum surrounded and molybdenum supported palladium nanoparticles, using a 10m2g−1 alumina support. These samples were tested for their active surface area using carbon monoxide chemisorption and their retention of hydrogen through temperature programmed desorption. Samples are also tested for their activity in the oxidation of carbon monoxide and the selective hydrogenation of 1-pentyne. Samples demonstrate high (95%) selectivity to the formation of 1-pentene as seen previously. Molybdenum containing structures demonstrate a slight activity suppression and associated selectivity increase. Molybdenum surrounded and nucleated particles demonstrate an increased resistance to sintering with little eﬀect on catalytic activity. This work demonstrates the use of a simple technique to quickly produce large (across 30m2) structures for lab scale catalytic testing.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):