The Catalyst Review July 2019 - 15

EXPERIMENTAL
graphitic frame-works. The GOMC retained the parental hexagonal periodic mesostructure of the silica template as revealed by
the small-angle X-ray diffraction (XRD) patterns The transmission
electron microscopy (TEM) image of the GOMC shows a hexagonal array of carbon nanorods with a diameter of about 9 nm
(Figure 1a).

Figure 1. a) Side-view TEM image of the GOMC (inset: top-view TEM image,
scale bar: 25 nm). High-resolution TEM image of b) the GOMC and c) CNT with
representations for each carbon. d) XRD patterns, e) Raman spectra, and f) C 1s
XPS spectra of the GOMC and CNT.

The electrocatalytic performances of the GOMC and CNT for
H2O2 production via ORR were examined in 0.1 M KOH using the
rotating ring-disk electrode (RRDE) technique. The polarization
curves of the catalysts presented in Figure 2a reveal that the
GOMC exhibits a much higher ORR activity than that of the CNT,
indicated by a positive shift of the onset potential by 65 mV in
the GOMC (0.78 V vs. reversible hydrogen electrode; RHE). Also,
they found, that the heterogeneous electron transfer kinetics of
the carbon-based catalyst is closely related to the electrocatalytic
activity, suggesting that first outer-sphere electron transfer to
O2 is an important step governing the H2O2 production rate.
Figure 2. a) Polarization curves of the GOMC and CNT for the ORR (c) and H2O2 production (a) measured in O2-saturated 0.1m KOH at an electrode rotation speed
of 1600 rpm and b) corresponding Tafel plots for the H2O2 production. The peroxide current was calculated by the correction of the ring current with the collection
efficiency of the RRDE. c) H2O2 selectivity determined using the RRDE method.

Source: Sa YJ, Kim JH, and Joo SH. (2019). Angew. Chem. Int. Ed., 58: 1100 -1105.
Enhanced Performance for Selective Catalytic Reduction of NOx with NH3 over Nanosized
Cu/SAPO-34 Catalysts...
Efforts to remove nitrogen oxides (NOx) from the exhaust of vehicles have centered on the use of selective catalytic reduction of NOx
with NH3 (NH3-SCR) due to high efficiency and low secondary pollution. Transition metal-exchanged zeolites (e.g., Cu/ZSM-5, Cu/
Beta) have been employed, but the structures of these catalysts are prone to collapse towards hydrothermal conditions. Recently,
SCR catalysts based on small-pore Cu-exchanged Chabazite (Cu-CHA) zeolites, such as Cu/SSZ-13, Cu/SAPO-34, and Cu/SAPO-44 have
been widely studied because of their excellent catalytic activity and hydro-thermal durability. So far, various synthetic methods have
been employed to prepare Cu/SAPO-34 catalysts, including impregnation method, traditional solution ion-exchange method, solidstate ion exchange and in situ hydrothermal synthesis method (which has proven to be the most economically viable). The NH3-SCR
performance is mainly affected by the hydro-thermal stability of catalysts, and the state and content of active sites which in the case
of Cu/SAPO-34 catalysts, include Lewis acid (from Cu ions) and Brønsted acid (from zeolites) sites. In this work, the authors studied
the influence of synthetic method, Brønsted acidity, as well as crystal size of Cu/SAPO-34 catalysts on the NH3. A series of nanosized
Cu/SAPO-34 catalysts with different silicon contents were successfully synthesized by an in-situ hydrothermal method by using
tetraethylammonium hydroxide and copper-tetraethylenepentamine as co-templates (Scheme 1). The in situ prepared nanosized
Cu/SAPO-34 catalysts possess strong Brønsted acidity and well-dispersed Cu species, showing enhanced performance for selective
catalytic reduction of NOx with NH3 compared with micron-sized and nanosized counterparts prepared by post-impregnation
method (Figure 1). The authors found that an increase of Brønsted acid sites in Cu/SAPO-34 facilitates the exchange of Cu and the
adsorption of ammonia, which improves the catalytic activity in NH3-SCR. Compared with the impregnation method, in situ synthesis
The Catalyst Review

July 2019

The Catalyst Review July 2019

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