A Highly Stable Copper‐Based Catalyst for Clarifying the Catalytic Roles of Cu⁰ and Cu⁺ Species in Methanol Dehydrogenation

Abstract

Identification of the active copper species, and further illustration of the catalytic mechanism of Cu-based catalysts is still a challenge because of the mobility and evolution of Cu and Cu species in the reaction process. Thus, an unprecedentedly stable Cu-based catalyst was prepared by uniformly embedding Cu nanoparticles in a mesoporous silica shell allowing clarification of the catalytic roles of Cu and Cu in the dehydrogenation of methanol to methyl formate by combining isotope-labeling experiment, in situ spectroscopy, and DFT calculations. It is shown that Cu sites promote the cleavage of the O-H bond in methanol and of the C-H bond in the reaction intermediates CH O and H COOCH which is formed from CH O and HCHO, whereas Cu sites cause rapid decomposition of formaldehyde generated on the Cu sites into CO and H .

Catalytic Performances of Cu/MCM-22 Zeolites with Different Cu Loadings in NH3-SCR

“…As presented in Figure 6A, at least five peaks can be distinguished in the Cu 2p XPS spectra of xCu/MCM-22 zeolites. According to the literature [62][63][64][65], the Cu 2p 3/2 peak at around 933 eV, the Cu 2p 1/2 peak at around 953 eV and the 2p → 3d satellite peak at around 944 eV confirm the existence of CuO species in xCu/MCM-22 zeolites, which is in accordance with the above XRD, UV-vis and H 2 -TPR results. Moreover, the asymmetry of the Cu 2p 3/2 peak at about 933 eV can be deconvoluted into two contributions centered around 933 and 935 eV (as shown in Figure 6B-F), corresponding to dispersed CuO and CuO species which have electrostatic interactions with MCM-22 zeolite framework, respectively, according to previous reports [63][64][65].…”

In situ tuning of electronic structure of catalysts using controllable hydrogen spillover for enhanced selectivity

“…Some researchers have devoted substantial effort to studying how to control and tune the electronic structures of the active sites responsible for activity and selectivity under real reaction conditions 9,10 . In contrast to numerous studies on identifying catalytically active sites under real-time reaction conditions [11][12][13][14] , limited methods have been reported for controlling and tuning the electronic structure of active sites during a reaction.…”

Copper–Zirconia Catalysts: Powerful Multifunctional Catalytic Tools to Approach Sustainable Processes

“…A good reducibility is critical to suppress the surface oxidation, as metallic Cu is the active center for the molecular hydrogen activation, in MS, or formation, in MSR and MD. Third, Cu + species, whose role in the reactions has been the specific object of several studies [14,68,69], are not stable under reducing environment but can be stabilized by introduction into the zirconia lattice as they compensate for the negative charge of oxygen vacancies [70].…”

“…From the vast work by Bell and co-workers [18,61,62,67,72] at the end of the 1990s, to the more recent investigations by Yang et al [69] and Larmier et al [41], just to cite but a few, great advancements have been made in understanding the complete picture of the surface chemistry during reactions with methanol. The main difference between methanol formation (MS) and hydrogen production reactions (MSR and MD) lays in the reactants, meaning that the first step of the catalytic process consists of the adsorption of CO 2 (or CO) and H 2 in the former, and of methanol and water in the latter.…”

“…The presence of Cu + sites has been for long considered necessary to the MSR reaction [14,78,96,99,100], and Yang et al [69] have clarified their decisive role in the dehydrogenation of the methoxy intermediates. Similar to the MS reaction, these sites basically act as Lewis centers [9].…”