activation (catalyst)	The procedure whereby a catalyst is put into a state (activated state) which can catalyze the reaction. Depending on the reaction at hand, this can be, for example, reduction (active phase = metal) or sulfidation (active phase = sulfide).
active site	An ensemble of atoms on the catalyst which directly catalyzes a reaction.
activity (catalyst)	Catalytic activity refers to the reaction rate, i.e., the speed at which a reaction takes place. This is typically quantified by turnover frequency (TOF).
calcination	The process of heating a sample, in this context a catalyst, to high temperature under an oxygen or air environment.
cavitation bubble	A small bubble, typically with sizes on the order of µm–mm, that can collapse explosively and generate a localized increase in pressure (e.g., shock waves) and temperature. In the case of sonication (ultrasound) of a liquid, these bubbles originate from rapid compressions and expansions of the liquid medium.
chemical reduction (colloidal synthesis)	A colloidal synthesis protocol whereby reduction to zerovalent state of the metal is achieved-in part-through the addition of a reducing agent.
coking	The process whereby cokes are formed, i.e., carbonaceous species, as undesired by-products of a reaction. As cokes occupy active sites, this leads to catalyst poisoning.
colloid	A type of mixture whereby solid or liquid particles, in the range of 1–1000 nm, are dispersed in a liquid phase and surrounded by a protective layer which prevents their agglomeration.
conformal	With even thickness over the exposed surface.
conversion (of a reagent)	In reaction engineering, the conversion of a reagent is defined as the ratio of [the number of moles of a certain reagent that have reacted] over [the initial number of moles of reagent].
core-shell	An architecture consisting of a core material (A) surrounded by a concentric shell of a second material (B). Typically denoted as A@B.
crystal facet	A planar side of a geometrical shape.
deactivation (catalyst)	The process whereby a catalyst loses its activity over time. Typical deactivation phenomena include coking and metal sintering.
embedded nanoparticles	Nanoparticles which are located within the support material, rather than on the support’s surface.
in situ reduction (colloidal synthesis)	Colloidal deposition protocol whereby the colloidal synthesis takes place in the presence of the support.
incipient wetness impregnation	Catalyst synthesis protocol whereby the metal precursor is first dissolved in a solvent, after which this dissolved precursor is added to the support. Herein, the volume of solution used is the same as the support pore volume.
Janus-like architecture	Nanoparticle architectural pattern that exhibits two distinguishable subunits. For instance, in a bimetallic CoFe particle, one subunit can exhibit low Co concentration, whereas the other subunit exhibits much higher Co concentration.
mesoporous	Containing pores with pore diameters between 2 and 50 nm.
metal precursor	A compound that contains a metal in its ionic state and serves as the metal source for catalyst synthesis.
microporous	Containing pores with pore diameters smaller than 2 nm.
monodisperse distribution	Displaying a narrow distribution. Synonym for uniform.
multimetallic	In this paper, multimetallic refers to any composition that contains more than 3 metals.
nanoparticle	A particle in the nanoscale regime, i.e., 1–100 nm.
nucleation	The initial process whereby a novel phase starts growing within or onto a pre-existing phase.
organometallic salt	A substance which is partially ionic (in the case of a metal precursor, this is a metal ion) and partially organic. An example is Ni(acac)2, made up of Ni2+ with surrounding (organic) acetylacetonate (acac) groups.
performance (catalyst)	A catalyst’s performance refers to its behavior during reaction. Commonly quantified via the terms reagent conversion, product selectivity, product yield, activity and stability.
poisoning (catalyst)	The act of blocking active sites of a catalyst with unwanted material, e.g., cokes, thus inhibiting contact of these active centers with reagents, which is detrimental to the catalytic activity.
promoter (catalyst)	A substance added to a catalyst to improve its performance.
protective agent	A chemical agent used in colloidal synthesis. It has a dual purpose: controlling the nanoparticle growth (capping agent) and preventing coalescence of colloidal nanoparticles (stabilizing agent).
rational/knowledge-driven catalyst design	The design of novel and improved catalysts in an efficient and cost-effective way. The creation of monodisperse materials helps to achieve this goal as follows. Materials with well-defined properties (e.g., nanoparticle size) allow investigating the effect of this property on the catalytic performance for a given reaction. As such, the optimal catalyst property (e.g., size which gives maximum activity) can be identified, which gives guidelines (knowledge) for the design of a new and improved catalyst.
reactant (ALD)	One of the two main components, besides a metal precursor, making up an ALD cycle. Reactants typically are gases, e.g., H2O, NH3, H2S, O3 etc., which, unlike the metal precursor, do not contain any metals.
reducing agent	A chemical added during colloidal synthesis (in chemical reduction protocols) which helps implement the reduction of the metal ions to their zerovalent state
selectivity (towards a product)	In reaction engineering, the conversion of a reagent is defined as the ratio of [the number of moles of the product that have formed] per [mole of reagent that has reacted].
self-limiting surface reaction	A surface reaction which stops when the surface is depleted of functional groups.
single crystal	A solid wherein an orderly three-dimensional arrangement of atoms is repeated throughout the entire material.
sintering	The thermally-induced process whereby small particles coalesce to form bigger particles. When this occurs for the nanoparticles in a catalyst, this leads to lower surface area of the active phase.
stability (catalyst)	A term denoting to what degree a catalyst retains its (initial) performance after a certain reaction time. Typically measured by monitoring the performance over an extended reaction time and observing the changes in activity/selectivity/conversion/etc. relative to initial values.
structure-sensitive reaction	A reaction of which the reaction kinetics are dependent on the surface structure of the catalyst.
support	A solid material, onto which the active nanoparticles are fixed, supplying mechanical strength and a large area to disperse the active phase. Sometimes also called substrate, though this latter term is more used in the context of planar support materials.
thermal decomposition (of an organometallic metal precursor)	A type of colloidal synthesis protocol whereby the metal precursor is organometallic in nature, e.g., an organometallic salt, and, through exposure to high temperatures, is decomposed and (thermally) reduced to its zerovalent state.
turnover frequency	A measure used to quantify the number of reagent conversions an active site performs per second.
wet impregnation	Catalyst synthesis protocol whereby the metal precursor is first dissolved in a solvent, after which this dissolved precursor is added to the support. Herein, the volume of solution used is much larger than the support pore volume.
yield (of a product)	In reaction engineering, the yield of a product is defined as the ratio of [the number of moles of the product that have formed] over [the initial number of moles of reagent]. Mathematically, this follows from multiplying the reagent conversion with the product selectivity.