No abstract

Although noble metal or non-noble metal-catalyzed reactions are widely used, it is still difficult to apply these reactions in the large-scale synthesis of chemicals because most of the reactions are carried out by the inefficient batch reaction strategy. Herein, Pickering emulsion-based continuous flow catalysis was utilized to address this problem. Cellulose nanofibers with aldehyde groups (ACNF) were generated through oxidizing C2 and C3 hydroxyl groups of cellulose nanofibers into aldehyde groups by NaIO 4 , followed by in situ depositing Ag nanoparticles on ACNF to produce Ag-decorated ACNF (ACNF@Ag) via a facile aldehyde-induced reduction method. ACNF@Ag with ∼2 wt % Ag (ACNF@Ag2) has been used to prepare the Pickering emulsion by controlling the electrostatic interaction between ACNF@Ag2 and the oil−water interface via adjusting the pH. It was found that the Pickering emulsion could be generated at a pH around 3.29 and was determined to be the oil-in-water emulsion. The reduction of organic molecules (4-nitrophenol (4-NP), methylene blue (MB), and methyl orange (MO)) was selected as a model reaction to test the reliability of the Pickering emulsion in continuous flow catalysis, which demonstrated very high conversion rates for 4-NP (>98%, 50 h), MB (>99%, 30 h), and MO (>96%, 40 h).

Continuous flow catalysis is favored for large‐scale chemical synthesis due to its time‐saving, energy‐saving, and cost‐efficient characters. Herein, Pickering emulsions are demonstrated to be effective carriers for immobilizing metal nanocatalysts in continuous flow catalysis. A series of metal nanoparticles (Pd, Au, and Pt) are coated on emulsion droplets via a facile aldehyde‐induced reduction method. Meanwhile, Pickering emulsion can be formed by using aldehyde cellulose nanofibers (ACNFs) with different dimensions that come from eucalyptus wood, cotton, and bacteria cellulose. These ACNFs can be entangled together to generate an interfacial layer for locking in emulsion droplets and providing reactive sites for in situ growth of metal nanocatalysts. In Pd‐anchored emulsion, the continuously catalytic reduction of 4‐nitrophenol (4‐NP), methylene blue, and methyl orange can proceed effectively for 55, 23, and 50 h with the conversion efficiencies at nearly 100%, >98%, >99%, respectively. In addition, Au‐ and Pt‐deposited emulsions are also operable in continuous flow catalysis as demonstrated by catalytic reduction of 4‐NP. Au‐decorated emulsion ensures the proceeding of catalytic reduction for 45 h with the conversion efficiency of >98% while Pt‐immobilized emulsion allows for the reduction of 4‐NP for 50 h at a conversion efficiency of >99%.