2.1 Catalyst preparation
The Cu-based catalysts were synthesized using both ion exchange and
wetness impregnation methods, as illustrated in Supporting Information
(SI, section 1, Scheme S1). Commercial MOR zeolite (purchased from
Nankai University Catalyst Co., Ltd.) was calcined in a muffle furnace
at 400 °C for 5 hours.
Cu(CH3COO)2·H2O and
Cu(NO3)2·3H2O (provided
by Shanghai Aladdin Biotechnology Co.) were used as the copper sources
for ion exchange and wetness impregnation, respectively. For the ion
exchange method, 10 g MOR zeolite was added to 28 ml
Cu(CH3COO)2·H2O solution
(0.4molCu/l), stirred, and placed in a 90 °C water bath
for 2 hours. Then, the samples were
filtered, washed and dried overnight
at 100 °C. Subsequently, the dried samples were calcined in a muffle
furnace at 540 °C for 5 hours, yielding the ion-exchanged Cu-MOR,
designated as Cu-MOR IE-1. To further enhance the Cu loading, various
cycles of ion exchange (2, 3, 4, and 5) were used to synthesize Cu-MOR
catalysts based on the Cu-MOR IE-1 sample. These samples, prepared
through multiple ion exchanges, are denoted as Cu-MOR IE-2, Cu-MOR IE-3,
Cu-MOR IE-4 and Cu-MOR IE-5. The wetness impregnation method involved
dissolving Cu(NO3)2·3H2O
in deionized water, adding MOR zeolite to the solution with calculated
loading, and stirring intensively. After aging at room temperature for
12 hours, the samples were dried at 120 °C overnight and calcined in a
muffle furnace at 540 °C for 5 hours. Finally, the obtained samples are
denoted as X wt.% Cu-MOR (X = 2, 5, 10, 15, and 20) based on different
Cu loadings.