Maximizing the utilization of noble metals is crucial for applications such as catalysis. We found that the minimum loading of platinum for optimal performance in the hydroconversion of n -alkanes for industrially relevant bifunctional catalysts could be reduced by a factor of 10 or more through the rational arranging of functional sites at the nanoscale. Intentionally depositing traces of platinum nanoparticles on the alumina binder or the outer surface of zeolite crystals, instead of inside the zeolite crystals, enhanced isomer selectivity without compromising activity. Separation between platinum and zeolite acid sites preserved the metal and acid functions by limiting micropore blockage by metal clusters and enhancing access to metal sites. Reduced platinum nanoparticles were more active than platinum single atoms strongly bonded to the alumina binder.

The preparation of zeolite-based bifunctional catalysts with low noble metal loadings while maintaining optimal performance has been studied. We have deposited 0.03 to 1.0 wt % Pt on zeolite H-USY (Si/Al ∼ 30 at./at.) using either platinum(II) tetraammine nitrate (PTA, Pt(NH 3 ) 4 (NO 3 ) 2 ) or hexachloroplatinic(IV) acid (CPA, H 2 PtCl 6 ·6H 2 O) and studied the nanoscale Pt loading heterogeneities and global hydroconversion performance of the resulting Pt/Y catalysts. Pt/Y samples prepared with PTA and a global Pt loading as low as 0.3 wt % Pt ( n Pt / n A = 0.08 mol/mol, where n Pt is the number of Pt surface sites and n A is the number of acid sites) maintained catalytic performance during n -heptane ( T = 210–350 °C, P = 10 bar) as well as n -hexadecane ( T = 170–280 °C, P = 5 bar) hydroisomerization similar to a 1.0 wt % Pt sample. For Pt/Y catalysts prepared with CPA, a loading of 0.3 wt % Pt ( n Pt / n A = 0.08 mol/mol) sufficed for n -heptane hydroisomerization, whereas a detrimental effect on n -hexadecane hydroisomerization was observed, in particular undesired secondary cracking occurred to a significant extent. The differences between PTA and CPA are explained by differences in Pt loading per zeolite Y crystal (size ∼ 500 nm), shown from extensive transmission electron microscopy energy-dispersive X-ray spectroscopy experiments, whereby crystal-based n Pt / n A ratios could be determined. From earlier studies, it is known that the Al content per crystal of USY varied tremendously and that PTA preferentially is deposited on crystals with higher Al content due to ion-exchange with zeolite protons. Here, we show that this preferential deposition of PTA on Al-rich crystals led to a more constant value of n Pt / n A ratio from one zeolite crystal to another, which was beneficial for catalytic performance. Use of CPA led to a large variation of Pt loading independent of Al content, giving rise to larger variations of n Pt / n A ratio from crystal to crystal that negatively affected the catalytic performance. This study thus shows the impact of local metal loading variations at the zeolite crystal scale (nanoscale) caused by different interactions of metal precursors with the zeolite, which are essential to design and synthesize optimal catalysts, ...

Ta ndemcatalysis combines multiple conversion steps, catalysts, and reagents in one reaction medium, offering the potential to reduce waste and time. In this study,P ickeringe mulsionsemulsions stabilized by solidp articles-are used as easy-topreparea nd bioinspired, compartmentalized reaction media for tandemc atalysis. Making use of simple and inexpensive acid and base catalysts, the strategy of compartmentalization of two noncompatible catalysts in both phases of the emulsion is demonstrated by using the deacetalization-Knoevenagel condensation reaction of benzaldehyde dimethyl acetal as a probe reaction. In contrast to simple biphasic systems, which do not allow for tandem catalysis and show instantaneous quenching of the acid and base catalysts, the Pickering emulsions show efficient antagonistic tandemc atalysis and give the desired product in high yield, as ar esult of an increased interfacial area and suppressed mutual destruction of the acid and base catalysts.Biomimicry,t hat is, science inspired by biological entitiesa nd processes, has served catalysis well, for instanceb ym imicking enzyme active sites for the development of new atom-efficient conversionsa nd the design of new biomimetic catalysts. [1] However,l ess attention has been given to bio-inspiredr eactor and process design, emulating the efficiency with which living cells are capable of performing multiple sequential and parallel reactions simultaneously. [2] In this study,w ea im to emulaten ature's strategy of compartmentalization to efficiently perform coupled, one-potr eactions and, in particular,t oa llow antagonistic orthogonal tandem catalytic reactions. [3,4] Orthogonal tandemc atalysis has been defined by Lohr et al. as ao ne-pot reactioni nw hich sequentialc atalytic processes occur through two or more functionally distinct, and preferably non-interfering catalytic cycles. [4] The major challenge of operating tandemr eactions for non-interfering catalysts is that the optimal process param-eters and kinetic regimes for each are typicallyq uite different. Furthermore, noninterference cannot always be avoided and catalystnon-compatibility in fact offers another main challenge for efficient tandem catalysis, for example when combining antagonistic catalysts such as an acid andabase. In that case, the two catalysts need to be kept physically separate, but still be accessible fort he substrates. Various approaches have been taken towards the design of bifunctional acid-base catalysts, often relying on the spatial separation of the reactive entities on polymeric or oxidic support materials, [5,6] for example, in the form of yolk-shellm aterials, [7] metal-organic frameworks (MOFs), [8][9][10][11] shell cross-linked micelles, [12,13] or star polymers. [14] An alternative strategy is to use bio-inspired reaction media and process options in which compartmentalization can be reversibly induced to physically separate soluble antagonistic catalysts. Herein, we reporto ns uch ac ompartmentalization approachi nt he form of aP ickering emulsion ...

Supported nickel nanoparticles are promising catalysts for the methanation of CO2. The role of nickel particle size on activity and selectivity in this reaction is a matter of debate. We present a study of metal particle size effects on catalytic stability, activity and selectivity, using nickel on graphitic carbon catalysts. Increasing the Ni particle size from 4 to 8 nm led to a higher catalytic activity, both per gram of nickel and normalized surface area. However, the apparent activation energy remained the same (∼105 kJ mol−1). Comparing experiments at atmospheric to 30 bar pressure demonstrates the importance of testing under industrially relevant pressures; the highest selectivity is obtained at high CO2 conversions and pressures. Finally, the selectivity was particle size‐dependent. The largest particles were not only most active but also most selective to methane. With this work we contribute to the ongoing debate about Ni particle size effects in CO2 methanation.

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Bifunctional catalysts containing a dehydrogenation–hydrogenation function and an acidic function are widely applied for the hydroconversion of hydrocarbon feedstocks obtained from both fossil and renewable resources. It is well known that the distance between the two functionalities is important for the performance of the catalyst. In this study, we show that the heat treatment of the catalyst precursor can be used to steer the location of the Pd precursor with respect to the acid sites in SAPO-11 and ZSM-22 zeotype materials when ions are exchanged with Pd(NH3)4(NO3)2. Two sets of catalysts were prepared based on composite materials of alumina with either SAPO-11 or ZSM-22. Pd was placed on/in the zeotype, followed by a calcination-reduction (CR) or direct reduction (DR) treatment. Furthermore, catalysts with Pd on the alumina binder were prepared. CR results in having more Pd nanoparticles inside the zeotype crystals, whereas DR yields more particles on the outer surface of the zeotype crystals as is confirmed using HAADF-STEM and XPS measurements. The catalytic performance in both n-heptane and n-hexadecane hydroconversion of the catalysts shows that having the Pd nanoparticles on the alumina binder is most beneficial for maximizing the isomer yields. Pd-on-zeotype catalysts prepared using the DR approach show intermediate performances, outperforming their Pd-in-zeotype counterparts that were prepared with the CR approach.