Spatially resolved quantitative surface characterization of grafted Ni catalysts inside nanochannels of anodic alumina membranes

• Nickel catalyst surface functionalization of an anodic aluminum oxide membrane. • XPS quantitative assessing Ni single atom catalyst distribution inside nanochannels. • Full monolayer surface coverage of 0.73 molecules/nm 2 from geometrical constraints. • Catalyst density gradient along the nanopores with decreased amount in the center. • Promising nanoscale reactors for low-branched polyethylene polymerization. Anodic aluminum oxide (AAO) mesoporous membranes functionalized with α-diimine Ni(II) complexes were recently considered as nanoscale chemical reactors for confined-space polymerization of ultra-high molecular weight, low-branched polyethylene. One of the factors regulating the structure–property relationship of the polymer is the spatial distribution of Ni single-atom catalysts present inside the membrane’s nanochannels. The grafting of the Ni complex inside the nanochannels occurs via the functional linker trimethylaluminum. Here, we employ X-ray photoelectron spectroscopy (XPS) to investigate and quantify both the distribution and absolute surface concentrations of the catalyst inside and along the nanochannels across the membrane. Up to 0.6 catalyst molecules/nm 2 have been detected in the middle of the nanochannels. This value corresponds to approximately 80% of the maximal monolayer surface coverage of 0.73 catalyst molecules/nm 2 found outside the pores, i.e. on the flat membrane surface. This work not only demonstrates that it is possible to graft functional catalysts inside the confined space of nanochannels, but it also quantifies their surface concentrations. This quantitative mapping establishes a critical foundation for the design of nanochannel reactors with tailored catalyst distributions. We found catalyst density gradients along the nanopores that could be useful to vary the density of polymerization sites along these nanochannels