Propylene is the second most important starting chemical in the petrochemical industry after ethylene. Unlike ethylene, propylene readily undergoes substitution reactions including polymerisation, oxidation, halogenation, hydrohalogenation, alkylation, hydration, oligomerization and hydroformylation, which lead to a wide variety of important downstream products. One of the principal uses of propylene is to produce key chemicals from selective oxidation. In 2016, the world annual production of propylene is about 94 million tonnes, and the global proportion used to produce selective oxidation product is over 18%. They constitute a key part of the chemical industry and contribute towards substantial economic benefits. The application of Ag based heterogeneous catalysts to selective propylene oxidation is a key factor in the synthesis of nearly all downstream chemicals, however billions of pounds are lost every year due to unplanned reactor shutdown, safety control and environment unfriendly emission control as a results of inefficiency catalytic selectivity and activity. Despite, both theoretical and experimental research works have been intensively involved, the fundamental reason leading to these effects are not yet well understood. The work presented in this thesis explores a range of novel modification techniques that alter the activity of Ag nanocatalysts for selective propylene oxidation, especially in propylene epoxidation. Particular focus is placed on developing surface modified Ag catalysts through morphology control, surface architecture engineering with another sublayer metal. Using a combination of modelling, novel and traditional materials characterisation methods, it is found that these modification result in some significant electronic and/or geometric alterations to the Ag nanoparticles surface. The Ag-Ag bond distance can be dramatically enlarged by exposing a high-index Ag surface or a core-shell structure with monolayer Ag shell. When interacting with molecular oxygen, the molecular oxygen adsorption and dissociation behaviour is sensitive to the geometric changes in Ag surface. This leads to an enhanced selectivity toward propylene epoxidation than combustion resulting from preventing a C-H bond cleavage. Finally, be creating atomically dispersed Ag on zeolite, a completely different interaction between molecular oxygen and single atom Ag were discovered comparing to on a extensive silver surface. This leads to the observation of an excitingly new propylene oxidation reaction producing ethanol and CO₂ resulting from C=C bond cleavage. Overall, the research presented within this thesis demonstrated a number of methods for the intelligent design of novel heterogeneous Ag catalysts with remarkable activity and selectivity toward specific selective propylene oxidation. These modification methods are believed to be potentially applicable to a wide range of other catalytic reactions.

<p dir="ltr">Additive manufacturing has introduced new possibilities for the design and manufacturing of monolith catalyst beds. Many hydrogen peroxide monolith catalyst beds are made of ceramics and washcoated through a complex process. However, creating a metal monolith bed with the tried-and-true silver catalyst could provide an alternative decomposition method for 90 wt.% hydrogen peroxide with easier manufacturing methods and similar or better decomposition efficiency. 91.2 wt.% hydrogen peroxide was decomposed with a lattice-type monolithic catalyst bed additively manufactured out of 316L stainless steel that was electroplated with pure silver. The variables investigated included the catalyst bed’s mass loading, chamber pressure, pressure drop, and length-to-diameter ratio (L/D). The catalyst bed had loadings of 0.1 lb_m/s/inch², 0.25 lb_m/s/inch², and 0.4 lb_m/s/inch². One catalyst bed configuration had an L/D of 2.6, while the other configuration had an L/D of 0.85. A modular throat controlled the chamber pressures for each catalyst bed loading case. The decomposition efficiency was calculated with the theoretical and expected characteristic velocity (c*) of the catalyst beds. The chamber pressures for the lowest bed loading and highest L/D ratio varied from 52 psia to 202 psia. The hydrogen peroxide decomposition efficiency was approximately 85% for the lowest chamber pressure and approximately 100% for the highest chamber pressure. The chamber pressures for the middle and highest bed loading and high L/D were 193 psia at the lowest to 325 psia at the highest. The decomposition efficiencies for all middle and highest bed loading tests with high L/D were 90% or higher for all tests. For all of the highest L/D tests, decomposition was also confirmed by observing videos of the exhaust plume, which was clear and showed no sign of flow channeling. For all of the highest L/D tests, the pressure drops in all of the middle bed loading cases were at or below 30% of the chamber pressure. The high chamber pressure, highest bed loading cases also had a pressure loss below 30% of the chamber pressure. The smallest L/D configuration performed significantly worse than expected, with efficiencies between 15-25% at chamber pressures between 33-75 psi. The silver electroplated on the stainless steel survived the 143 s of lifetime on the catalyst bed during testing with minimal to no silver loss determined by weight and visual inspection with a microscope post-test. The higher L/D catalyst bed tests prove that silver electroplated on to an additively manufactured stainless steel monolith is a viable method for creating a catalyst bed. More research is required to determine the lowest L/D possible, which resides somewhere between the two L/D cases studied, and higher bed loadings also require investigation.</p>