Ammonia is a promising hydrogen carrier for producing COx-free hydrogen. However, its decomposition suffers from high reaction temperatures. This study reveals that trace Ga doping markedly boosts the low-temperature activity of Ni/Al2O3 catalyst for ammonia decomposition. The Ga-doped Ni/Al2O3 catalyst achieves 92.0% ammonia conversion at 500 oC and weight hourly space velocity (WHSV) = 30,000 mL gcat−1 h−1. Kinetic experiments demonstrate that the introduction of Ga species alleviates catalyst hydrogen poisoning. Further studies confirm that Ga preferentially segregates on the catalyst surface and disperses around Ni nanoparticles. Interfacial Ga species facilitate hydrogen spillover from Ni to the Al2O3 support, which promotes the enrichment of adsorbed N* species and reduces their recombination temperature on the Ni surface. This work develops an efficient and stable Ni-based catalyst for low-temperature ammonia decomposition and provides a strategy for optimizing catalytic performance via the regulation of interfacial hydrogen transfer. Ammonia could enable carbon-free hydrogen production, but efficient decomposition at low temperatures remains difficult. Trace gallium helps nickel catalysts remove surface hydrogen, markedly boosting low temperature activity.
Crucial for coastal carbon sequestration, global seagrass organic carbon (OC) burial rates remain uncertain as early estimates were derived from mixed methodologies across geographically and taxonomically biased datasets. Here, we present a data-driven reassessment from a synthesis of 332 sediment cores spanning the last century. Results show that seagrasses bury OC at 25 ± 3 g OC m−2 yr−1 (geometric mean), with an area-weighted global average of 33 ± 9 g OC m−2 yr−1. Rates reflect a balance between sediment OC content and sediment accumulation, which share a negative exponential relationship driven by mineral dilution. Based on a revised mapped seagrass extent (247,700–366,400 km2), global burial scales to 6–15 Tg C yr−1. Although one-fourth of earlier benchmarks, seagrasses account for 3–4% to 3–6% of total oceanic OC burial despite covering <0.1% of the seafloor. Combined with mangroves and tidal marshes, vegetated coastal ecosystems contribute 8–13% of oceanic OC burial. Reassessing global seagrass carbon burial via 332 sediment cores reveals an area-weighted average of 33 ± 9 g OC m-2 yr-1 (6-15 Tg C yr-1 globally). Despite covering <0.1% of the seafloor, seagrasses drive 3-6% of total oceanic organic carbon burial.
Optimizing the photothermal conversion (maximized solar absorption, minimized mid-infrared emissivity) and catalytic activity is essential for constructing highly efficient photothermal catalysts. However, most catalysts lack intrinsic optical selectivity (i.e., high αsolar and low εMIR) and fail to suppress εMIR, which significantly compromises their catalytic performance. Herein, we propose an optical depth strategy to drive catalysts to their intrinsic optical selectivity limit. Demonstrated in metal oxides, this approach simultaneously maximizes αsolar and minimizes εMIR without compromising intrinsic catalytic activity. Demonstrated in the photothermal Sabatier and Bosch processes, our strategy increases methane production by ~590% and carbon nanotube yield by ~200%. Notably, the optimized Co2.85Ru0.15O4 optically selective catalyst exhibits a ~ 26.7% increase in photothermal conversion efficiency. This enhancement leads to a record CH4 production rate of 3375.5 mmol gcat−1 h−1 at a light intensity of 2.8 W cm−2. This innovative strategy highlights the prospects for achieving intrinsic optical selectivity in photothermal catalysts. Optimizing photothermal conversion and catalytic activity is crucial for developing highly efficient photothermal catalysts. Here, the authors propose an optical-depth strategy to drive catalysts toward their intrinsic optical selectivity limit, thereby enhancing the efficiency of photothermal catalysis.
