Elucidating the Nature of Active Sites and Fundamentals for their Creation in Zn-Containing ZrO₂–Based Catalysts for Nonoxidative Propane Dehydrogenation

Abstract

Environmentally friendly and low-cost catalysts are required for large-scale non-oxidative dehydrogenation of propane to propene (PDH) to replace currently used CrO x -or Pt-based catalysts. This work introduces ZnO-containing ZrO 2 -or MZrO x -supported (M=Ce, La, Ti or Y) catalysts. The most active materials outperformed the state-of-the-art catalysts with supported CrO x , GaO x , ZnO x or VO x species as well as bulk ZrO 2 -based catalysts without ZnO. The spacetime yield of propene of 1.25 kg C3H6 •kg -1 cat •h -1 at a propane conversion of about 30% with propene selectivity of 95% was obtained over Zn(4 wt%)/TiZrO x at 550°C.For deriving key insights into the structure of active sites, reactivity, selectivity and onstream stability, the catalysts were characterized by XRD, HRTEM, EDX mapping, XPS, X-ray absorption, CO-TPR, CO 2 -TPD, NH 3 -TPD, Pyridine-FTIR, operando UV-Vis spectroscopy, Raman spectroscopy, TPO and temporal analysis of products. In contrast with previous reports used bulk ZrO 2 -based catalysts without ZnO, coordinatively unsaturated Zr cations are not the main active sites in the ZnO-containing catalysts.Supported ZnO x species were concluded to participate in the PDH reaction. The current X-ray absorption analysis proved that their structure is affected by the type of metal oxide used as dopant for ZrO 2 and on crystallinity of ZrO 2 . Isolated tricoordinated Zn 2+ species

In situ formation of ZnOx species for efficient propane dehydrogenation

“…15,16 ). Zn-containing catalysts were also tested but show commercially unattractive performance [17][18][19][20][21][22][23][24][25][26][27] . A general shortcoming of practically all supported catalysts developed until now is their economic inefficiency due to the complex preparation methods often requiring expensive chemicals.…”

Correlating the Structural Evolution of ZnO/Al2O3 to Spinel Zinc Aluminate with its Catalytic Performance in Propane Dehydrogenation

“…6 Metal oxide catalysts, including gallium, cobalt, aluminum and zinc oxide-based catalysts, are currently researched actively for the selective dehydrogenation of propane to propene. 2,[7][8][9][10][11][12][13] The metal sites on the surface of these oxides can exhibit different coordination environments and undergo changes in the oxidation state during the PDH reaction, which affect their catalytic performance. This has driven considerable research efforts to understand the active sites at the atomic level.…”

High‐Density Lewis Acid Sites in Porous Single‐Crystalline Monoliths to Enhance Propane Dehydrogenation at Reduced Temperatures

“…In contrast, the non‐oxidative propane dehydrogenation with noble‐metal catalyst like PtSn x gives the conversion of ≈50 % and the propylene selectivity of ≈90 % at ≈600 °C [8–13] . However, operation with non‐noble‐metal catalyst like VO X /Al 2 O 3 and VO X /ZrO 2 leads to a conversion below ≈25 % and a propene selectivity below ≈90 % even at ≈600 °C, while it suffers from serious coke deposition and conversion drop in dozens of minutes [14–17] . For non‐noble metal catalyst, the lack of catalytic activity gives rise to a limited propane conversion at reduced temperatures while the complicated functional groups at surfaces distract the main reaction to generate by‐products including methane, ethane and coke [18] .…”

“…[8][9][10][11][12][13] However, operation with non-noble-metal catalyst like VO X /Al 2 O 3 and VO X /ZrO 2 leads to a conversion below % 25 % and a propene selectivity below % 90 % even at % 600 8C, while it suffers from serious coke deposition and conversion drop in dozens of minutes. [14][15][16][17] For non-noble metal catalyst, the lack of catalytic activity gives rise to a limited propane conversion at reduced temperatures while the complicated functional groups at surfaces distract the main reaction to generate byproducts including methane, ethane and coke. [18] The high density of weak Lewis acid sites on the surface of catalyst is beneficial for the propane dehydrogenation reaction and could suppress the cracking reaction to avoid carbon deposition.…”