Abstract:We demonstrate the self-assembly of transition metal carbide nanoparticles coated with atomically-thin noble metal monolayers by carburizing mixtures of noble metal salts and transition metal oxides encapsulated in removable silica templates. This approach allows for control of the final core-shell architecture, including particle size, monolayer coverage, and heterometallic composition. Carbon-supported Ti0.1W0.9C nanoparticles coated with Pt or bimetallic PtRu monolayers exhibited enhanced resistance to sintering and CO poisoning, achieving an order of magnitude increase in specific activity over commercial catalysts for methanol electrooxidation after 10,000 cycles. These core-shell materials provide a new direction to reduce the loading, enhance the activity, and increase the stability of noble metal catalysts. One Sentence Summary:The self-assembly of transition metal carbide nanoparticles coated with atomically-thin noble metal monolayers results in a highly active, stable, and tunable catalytic platform.Noble metal (NM) catalysts critically enable many existing and emerging technologies, such as catalytic converters (1), reforming (2), and fuel cells (3). However, their scarcity and high cost necessitate the development of catalytic systems with reduced NM loadings, increased activity, and improved durability. In this respect, various nanostructured architectures have been investigated, including atomically-dispersed NM catalysts (4), hollow nanocages (5, 6), alloyed nanoparticles (NPs) (7), and core-shell structures (8, 9). In particular, core-shell NPs composed of an earth-abundant core coated with an atomically-thin NM shell are a promising platform that offers both design flexibility and reduced precious metal loadings. However, achieving independent control over the particle size, core composition, shell composition, and shell thickness poses a substantial challenge (8, 9). State-of-the-art synthetic methods are predominantly limited to a few earth-abundant metallic cores (e.g., Fe, Co, Ni, and Cu) that allow for more precise synthetic control; however, these metal cores form intrinsically metastable core-shell particles that restructure during heating (10-12) or electrochemical cycling (13, 14).Early transition metal carbides (TMCs) are earth-abundant ceramics with ideal topochemical properties for supporting precious metal shells (15-17). First, TMCs exhibit metallic electrical conductivity, corrosion resistance, and high melting points (18). Second, precious metals tend to bind strongly to metal-terminated early TMC surfaces (Fig. S1), but cannot readily form stable carbides (19). Thus, NMs should coat TMC surfaces, but should not alloy with the underlying core. In particular, tungsten carbide (WC) is inexpensive (Fig. S2), exhibits a "platinum-like" density of electronic states (20, 21), and its metal-terminated surface forms interfacial Pt-WC bonds that are ca. 90 kJ mol -1 stronger than interfacial Pt-Pt bonds (Fig. S1). Although experimental studies on model thin film systems have co...

Deactivation due to coking limits the lifetime of zeolite catalysts in the production of chemicals and fuels. Superior performance can be achieved through hierarchically structuring the zeolite porosity, yet no relation has been established between the mesopore architecture and the catalyst lifetime. Here we introduce a top-down demetallation strategy to locate mesopores in different regions of MFI-type crystals with identical bulk porous and acidic properties. In contrast, well-established bottom-up strategies as carbon templating and seed silanization fail to yield materials with matching characteristics. Advanced characterization tools capable of accurately discriminating the mesopore size, distribution and connectivity are applied to corroborate the concept of mesopore quality. Positron annihilation lifetime spectroscopy proves powerful to quantify the global connectivity of the intracrystalline pore network, which, as demonstrated in the conversions of methanol or of propanal to hydrocarbons, is closely linked to the lifetime of zeolite catalysts. The findings emphasize the need to aptly tailor hierarchical materials for maximal catalytic advantage.

We demonstrate that desilication in alkaline medium is a suitable post-synthetic method to introduce intracrystalline mesoporosity in MFI zeolites independent of the Si/Al ratio in the parent material. By systematic screening of the influence of both base concentration (0.1-1.8 M NaOH) and Si/Al ratio (10-1000) on the properties of the treated zeolites, we reveal that effective mesoporosity introduction Hierarchical ZSM-5 after acid washing stands as the most active sample, which stresses the relevance of the additional post-synthesis treatment step.

Mass transfer in zeolite crystals can be enhanced by the introduction of a hierarchical network of auxiliary mesopores. To fully exploit pore engineering in the design of more efficient industrial catalysts, the benefit needs to be demonstrated over technically relevant forms. Here, the influence of shaping on the adsorption and diffusion properties of hierarchical ZSM‐5 is assessed by studying the gravimetric uptake of 2,2‐dimethylbutane over powders and millimeter‐sized bodies. Formed by extrusion or granulation with clay binders, the latter display a complex trimodal network of micro‐, meso‐, and macropores. The enhanced intracrystalline diffusivity due to the interconnected mesopores is preserved in the macroscopic bodies, independent of the shaping method or binder applied. Furthermore the superior overall diffusivity is retained in the hierarchical bodies compared to their conventional (purely microporous) counterparts, despite the significant extracrystalline resistance to mass transfer. The connective participation of mesopores, leading to a 6 times improved effective diffusivity in hierarchical with respect to conventional zeolite powders, is revealed by the distinct dependence on the adsorbate concentration and the relationship with the mesopore surface area. Analysis of the thermodynamic parameters derived from the adsorption isotherm proves a sensitive method to detect binder‐zeolite interactions induced upon shaping.

Core-shell architectures offer an effective way to tune and enhance the properties of noble-metal catalysts. Herein, we demonstrate the synthesis of Pt shell on titanium tungsten nitride core nanoparticles (Pt/TiWN) by high temperature ammonia nitridation of a parent core-shell carbide material (Pt/TiWC). X-ray photoelectron spectroscopy revealed significant core-level shifts for Pt shells supported on TiWN cores, corresponding to increased stabilization of the Pt valence d-states. The modulation of the electronic structure of the Pt shell by the nitride core translated into enhanced CO tolerance during hydrogen electrooxidation in the presence of CO. The ability to control shell coverage and vary the heterometallic composition of the shell and nitride core opens up attractive opportunities to synthesize a broad range of new materials with tunable catalytic properties.

Decorating titanium tungsten carbide nanoparticles with sub-monolayer platinum surface coatings yields efficient and stable catalysts for hydrogen evolution/oxidation reactions in acidic media.

The manifestation of zeolite recrystallization and the formation of amorphous aluminosilicate species during desilication are examined to better understand the properties of alkaline-treated hierarchical zeolites and their catalytic performance. This is achieved using a systematic experimental strategy, starting from treating the filtrate of alkaline-treated silicalite-1 at different temperatures in the presence of various external additives. No recrystallization is evidenced upon addition of tetrapropylammonium (TPA + ) and/or aluminum hydroxide ions (Al(OH) 4 -),confirming the low probability of zeolite nucleation and/or growth during desilication.Conversely, ordered mesoporous materials (OMMs) form on addition of cetyltrimethyl ammonium (CTA + ) to the filtrate. By using other silicon sources, i.e. tetramethyl orthosilicate or the organosilane dimethyloctadecyl-[3-(trimethoxysilyl)propyl]-ammonium, we verify the facile formation of amorphous materials during alkaline treatment of USY zeolites in the presence of hydrophobic micelle-forming alkyl moieties. A systematic characterization by XRD, TEM, N 2 and Ar adsorption, ICP-OES, and FTIR spectroscopy of pyridine adsorbed demonstrates that zeolites exposed to base solutions containing CTA + display less zeolitic properties, compared to those prepared using TPA + , and should be considered as hierarchical zeolite/OMM composites.Catalytic tests in the alkylation of toluene with isopropyl alcohol or benzyl alcohol demonstrate that CTA + -derived composites do not outperform the conventional USY zeolite. Only the hierarchical USY zeolite prepared by alkaline treatment in the presence of TPA + yielded a superior catalytic performance.

are exposed to various acid and base treatments aimed at mesopore formation and investigation of associated physicochemical modifications. SAPOs amorphize strongly in aqueous NaOH, requiring the use of organic bases (e.g., tetrapropylammonium hydroxide or diethylamine) to preserve the crystallinity during base treatment. In acid media (HCl, H 4 EDTA, and Na 2 H 2 EDTA), SAPO-11 remains fully crystalline, while SAPO-34 strongly amorphize. No clear influence of the framework topology is established. The high resistance in alkaline media and low stability in acid media of SAPO-34 is attributed to its relatively high silicon content. Base treatment of SAPOs leads predominately to the formation of intercrystalline porosity. Still, an up to 4-fold increase in external surface and pore volume in SAPO-11 are achieved. Besides the formation of secondary porosity, base treatment of SAPOs induces a variety of (correlated) physicochemical changes. For example, the silicon distribution clearly influences the dissolution behavior of SAPO-11 in alkaline media, as zeolitic-like Si-domains are more resistant than AlPO domains. As a result, base leaching is selective to phosphorus and leads, depending on the silicon distribution, to either aluminum or silicon enrichment. The resulting changes in bulk composition can be directly related to the secondary porosity, as the Si and Al enrichment takes place predominately on the external surface. Acidity characterization (TPD of ammonia and IR spectroscopy of pyridine or 2,6-di-tert-butylpyridine adsorbed) shows that base treatment of SAPO-11 slightly reduces the concentration of Brønsted sites, while the number of Lewis sites is substantially increased. Moreover, the amount of Brønsted acid sites associated with the external surface is largely enhanced. The behavior of zeotypes, that is, AlPOs, SAPOs, and zeolites, in acid and basic aqueous solutions is generalized, highlighting the role of charge balancing cations. Catalytic evaluation of SAPO-11 shows the potential of base-treated samples in the alkylation of benzyl alcohol with toluene.