Toward Understanding the Manipulation of Surface Acidity Behavior with Relativistic Effect for the Formation of C–N Bonds

Abstract

To overcome the problems of stagnant activity and vulnerable acid sites, a meticulously tailored tetra-metallic catalyst, ScTiTbAuAPO-5, with an extremely low surface gold atom concentration of 0.02%, has been designed and prepared via one-step hydrothermal crystallization. It exhibits remarkable catalytic activity, leading to the direct condensation of aniline and C�X (X = O, N) blocks without extra assistance. The highest selectivity exceeds 99.00%. The highly dispersed stable metallic sites and the drastic surface polarization are the keys to unique catalytic performances, leading to high acid density and reversed acidity transformation behavior. In this synergistic system, scandium and titanium are the main active components, whereas terbium and gold regulate the acidity and activity via withdrawing electrons. The application of tetra-metallic synergy on the catalysis of C−N bond formation unveils a promising methodology to manipulate the surface acidity of the catalyst with the relativistic effect, dropping the consumption of noble metals simultaneously. The present work also exemplifies the immense potential of the multi-metallic synergistic strategy in green catalysis.

Mixed oxides with corundum-type structure obtained from recycling can seals as paint pigments: color stability

“…Using inorganic compounds in the synthesis tends to increase the chemical and physical stability of the pigments, ensuring greater durability. Furthermore, it reduces environmental problems because it avoids consuming natural raw materials, saving primary resources [ 10 – 11 ]. Inorganic pigments, generally, are less affected by light, ambient temperature, chemicals, and harsh atmospheres than organic pigments [ 12 ].…”

“…Global demand for pigments was around 12 million tons in 2020 and is dominated by titanium dioxide white pigment [ 11 ]. However, iron oxide red and chromium oxide green are technically important inorganic pigments due to color intensity, good dispersibility in paints, and superior hiding power [ 11 ]. Functionally, green is widely used as approval, while red is associated with prohibition and warning.…”

“…However, using boehmite as a host matrix, the opportunity arises to use chromium as a coloring ion to obtain the same color result, without using toxic precursors. Remarkably, iron oxide red belongs to the class of yellow, red, and brown ocher, whose color depends on the crystallographic phase [ 11 ]. The hematite phase (α-Fe 2 O 3 ) is the most stable, and its shade and color can be adjusted by the calcination temperature or the combination with other metals as coloring ions [ 11 ].…”

“…Remarkably, iron oxide red belongs to the class of yellow, red, and brown ocher, whose color depends on the crystallographic phase [ 11 ]. The hematite phase (α-Fe 2 O 3 ) is the most stable, and its shade and color can be adjusted by the calcination temperature or the combination with other metals as coloring ions [ 11 ]. In this context, applying both Cr and Fe ions as coloring ions in a white matrix such as aluminium oxide is interesting.…”