Silicalite-1 Stabilizes Zn-Hydride Species for Efficient Propane Dehydrogenation

Abstract

Propane dehydrogenation (PDH) is promising for producing high value-added propylene. The discovery of a more efficient, economical, and nontoxic PDH catalyst is of great importance. Herein, we found zinc hydrides ([ZnH]+) as the highly reactive site for PDH. In situ spectroscopy and theoretical studies reveal that [ZnH]+ was transformed from zinc hydroxyl ([ZnOH]+) sites under reductive conditions. Accordingly, the formation of [ZnH]+ can be controlled by adjusting the amount of zinc hydroxyl ([ZnOH]+) species by various additives. The optimized Cu–ZnO@S-1 consists of exclusively isolated [ZnOH]+ sites, which help produce more [ZnH]+ toward optimal PDH activity. Specifically, the catalyst enables 43% propane conversion with >88% propylene selectivity, close to the thermodynamic equilibrium. This efficient PDH performance was attributed to the electron-deficient Zn in [ZnH]+ that can lower the dehydrogenation barrier, and the Cu-modified [ZnH]+ structure favors the direct PDH pathway to further promote the formation of propylene and H2.

Manipulating the Cobalt Species States to Break the Conversion–Selectivity Trade-Off Relationship for Stable Ethane Dehydrogenation over Ligand-Free-Synthesized Co@MFI Catalysts

“…The mode of catalyst deactivation in alkane dehydrogenation mainly includes (1) coke deposition, (2) sintering of active metal sites, (3) transformation of active phase, and (4) losing of active metals, such as zinc , that can be sublimated at a high temperature. For a Co-based catalyst, the metal loss via sublimation into gas phase can be ignored, but the other three modes could take place in the reaction and should be considered seriously.…”

“…Because Cr is very harmful to the environment, in spite of its relative cheapness Cr-based catalysts are being phased out in the industry. Therefore, a large amount of non-noble-metal-based and environment-friendly catalyst systems for nonoxidative dehydrogenation were variously investigated, mainly including the first-row 3d (like V , and Zn − ) and group IIIA (like B, , Al, , Ga, , and In , ) metal-oxide-based catalysts.…”

“…With the same method, a Co-exchanged SAPO-34 zeolite, a kind of zeolite having a smaller pore size (0.34 nm) than HZSM-5 (0.55 nm), was also prepared and showed an extremely high selectivity to ethylene (∼99%) in ethane dehydrogenation (EDH) . In the recent 3 years, Fe ,, and, especially, Co ,,,− as the active sites have been showing their unique potential for alkane dehydrogenation because they are low-cost and not lost during reaction, different from the Zn-based catalysts. − However, the conversion–selectivity trade-off relationship in alkane dehydrogenation highly depends on the chemical states of these metals in a catalyst. Once metal oxides are easily reduced into zero-valent metal clusters, alkane decomposition would occupy an advantageous position (high conversion and low selectivity to olefins). , Therefore, for these group VIII metal-based dehydrogenation catalysts, construction of a stable −M δ+ –O δ− – structure is very crucial for selectively activating C–H bonds and suppressing C–C bonds.…”

Tuning product selectivity in the MTO reaction over Zn-modified SSZ-13 catalysts

“…7, Si, Al and Zn elements are uniformly distributed throughout the whole selected area without an evident phase separation, suggesting the homogeneous dispersion of Zn species in the form of isolated or single-site Zn. 40…”

B–O Oligomers or Ring Species in AlB2: Which is More Selective for Propane Oxidative Dehydrogenation?

“…Rapid weakening of the vibrational bands of the CH 2 group in propane (at 1472 and 1456 cm −1 ) suggests that the ODHP may be initiated by the cleavage of methylene C−H bonds 29 (Figure 4b). To prove this, the Vienna ab initio simulation package was used to simulate and determine the IR spectra of α-C and β-C adsorption (in *C 3 H 7 ) on R-AlB 2 (Figures 4c and S13).…”