Muhammad Zubair

Gallia-based shells with a thickness varying from a submonolayer to ca. 2.5 nm were prepared by atomic layer deposition (ALD) using trimethylgallium, ozone, and partially dehydroxylated silica, followed by calcination at 500 °C. Insight into the atomic-scale structure of these shells was obtained by high-field ⁷¹Ga solid-state nuclear magnetic resonance (NMR) experiments and the modeling of X-ray differential pair distribution function data, complemented by Ga K-edge X-ray absorption spectroscopy and ²⁹Si dynamic nuclear polarization surface enhanced NMR spectroscopy (DNP SENS) studies. When applying one ALD cycle, the grown submonolayer contains mostly tetracoordinate Ga sites with Si atoms in the second coordination sphere (^[4]Ga_(Si)) and, according to ¹⁵N DNP SENS using pyridine as the probe molecule, both strong Lewis acid sites (LAS) and strong Brønsted acid sites (BAS), consistent with the formation of gallosilicate Ga-O-Si and Ga-μ²-OH-Si species. The shells obtained using five and ten ALD cycles display characteristics of amorphous gallia (GaO_x), i.e., an increased relative fraction of pentacoordinate sites (^[5]Ga_(Ga)), the presence of mild LAS, and a decreased relative abundance of strong BAS. The prepared Ga1-, Ga5-, and Ga10-SiO_2-500 materials catalyze the dehydrogenation of isobutane to isobutene, and their catalytic performance correlates with the relative abundance and strength of LAS and BAS, viz., Ga1-SiO_2-500, a material with a higher relative fraction of strong LAS, is more active and stable compared to Ga5- and Ga10-SiO_2-500. In contrast, related ALD-derived Al1-, Al5-, and Al10-SiO_2-500 materials do not catalyze the dehydrogenation of isobutane and this correlates with the lack of strong LAS in these materials that instead feature abundant strong BAS formed via the atomic-scale mixing of Al sites with silica, leading to Al-μ²-OH-Si sites. Our results suggest that ^[4]Ga_(Si) sites provide strong Lewis acidity and drive the dehydrogenation activity, while the appearance of ^[5]Ga_(Ga) sites with mild Lewis activity is associated with catalyst deactivation through coking. Overall, the atomic-level insights into the structure of the GaO_x-based materials prepared in this work provide a guide to design active Ga-based catalysts by a rational tailoring of Lewis and Brønsted acidity (nature, strength, and abundance).

Controlled synthesis of Ni_2−xRh_xP nanoparticle catalysts enables an understanding of composition-dependent selectivity for the hydrodeoxygenation reaction of phenolic molecules.

Selective uranium extraction from seawater by dopant engineered layered double hydroxide.

Several transition metal oxides and hydroxides have been reported as active electrocatalysts towards the oxidation of 5-hydroxymethyl furfural (HMF), an important biomass-derived compound for downstream sustainable chemical and transport fuel production. However, few studies have investigated the activity descriptors influencing the reactivity and selectivity of these materials towards HMF electrooxidation (HMFOR). Herein, Co, Ni and Cu-based Prussian blue analogue (PBA) electrocatalysts were systematically investigated to identify the intrinsic electronic contributions of these redox species towards HMF electrooxidation activity. Cu-phase PBAs exhibited the highest faradaic efficiency of 97.4%, followed by Co-phase (90.5%) and Ni-phase (82.6%) PBAs towards generating 2,5-furandicarboxylic acid (FDCA) at 1.42 V vs. RHE in 1.0 M KOH. This activity trend is found to be influenced by the amount of nucleophilic OH* species expressed on the electrocatalyst's surface. A higher expression of these surface species results in a lower activation energy barrier for the rate limiting step, leading to increased selectivity towards FDCA. Analysis of the bulk electronic properties shows that a strong M–O bond covalency and high d-orbital occupancy contribute to this high expression of electrophilic sites. These findings establish a basis for rationalising the origins of FDCA selectivity in HMFOR catalysts, which importantly eschews using catalysts with high oxygen evolution reaction (OER) activity as a prerequisite for high HMFOR performance.

In situ pair distribution function measurements show that unlike analogous Au clusters, atom-precise Ag clusters fracture at high temperatures.

Coupled metal–nitrogen–carbon (M–N_x–C) materials show great promise as platinum-group-metal (PGM) free catalysts for the oxygen reduction reaction (ORR). Herein, we report a facile strategy to construct atomically dispersed Co–Fe dual sites enriched on the surface of nitrogen doped microporous carbon (NC) as an efficient electrocatalyst for ORR. Synchrotron X-ray techniques indicate that the Co and Fe atoms are strongly correlated while further revealing that the longer-range lattice structure of NC is highly tunable. Density functional theory calculations reveal that the Co–Fe dimers are incorporated in the slightly disordered NC substrate, providing a lower adsorption free energy for O₂. The as-prepared CoFe–NC catalyst exhibited excellent ORR activities, while a CoFe–NC based zinc–air battery exhibited a power density of 115 mW cm⁻² and a specific capacity of 791 mA h g⁻¹. This work showcases a straightforward methodology for creating atomically dispersed catalysts and illustrates the importance of understanding how dual metal sites impact electrocatalytic activity.

In this study, scalable, flame spray synthesis is utilized to develop defective ZnO nanomaterials for the concurrent generation of H₂ and CO during electrochemical CO₂ reduction reactions (CO₂RR). The designed ZnO achieves an H₂/CO ratio of ≈1 with a large current density (j) of 40 mA cm⁻² during long‐term continuous reaction at a cell voltage of 2.6 V. Through in situ atomic pair distribution function analysis, the remarkable stability of these ZnO structures is explored, addressing the knowledge gap in understanding the dynamics of oxide catalysts during CO₂RR. Through optimization of synthesis conditions, ZnO facets are modulated which are shown to affect reaction selectivity, in agreement with theoretical calculations. These findings and insights on synthetic manipulation of active sites in defective metal‐oxides can be used as guidelines to develop active catalysts for syngas production for renewable power‐to‐X to generate a range of fuels and chemicals.