Unraveling the Origins of the Synergy Effect between ZrO₂ and CrO_x in Supported CrZrO_x for Propene Formation in Nonoxidative Propane Dehydrogenation

Abstract

In this work, steady-state tests of propane dehydrogenation, density functional theory calculations, operando UV–vis spectroscopy, ex situ and in situ electron paramagnetic resonance spectroscopy, IR spectroscopy, and temperature-programmed techniques were combined to provide fundamentals for tuning activity and onstream stability of low-loaded catalysts with supported CrZrO x species. Two neighboring Zrcus (cus = coordinatively unsaturated) sites were concluded to be mainly responsible for propane dehydrogenation to propene. They are formed upon reductive catalyst treatment, and their concentration depends on the strength of interaction among CrO x , ZrO2, and support and on the size of ZrO2 crystallites in CrZrO x . SiO2 weakly interacting with CrO x was found to be a more preferable support than Al2O3- or TiO2-based supports. CrO x species promotes formation of Zrcus sites and improves their intrinsic activity for the desired reaction. CrO x also contributes to coke formation as concluded from operando UV–vis analysis. Cr20Zr80/SiO2 possessing about 3.9 or 2.5 times lower amounts of chromium or zirconium in comparison with an analogue of industrial K-CrO x /Al2O3 or state-of-the-art Ru/LaZrO x revealed about 2 times higher space-time yield of propene at 30% propane conversion at 550 °C. Moreover, this catalyst was durable over 50 dehydrogenation/regeneration cycles lasting 150 h.

Propane to olefins tandem catalysis: a selective route towards light olefins production

“…124 Indeed, modifications of CrO x /SiO 2 catalysts have been recently proposed either where chromium oxide is modified with zirconia or ceria, or where the support is different from silica, in order to enhance catalytic performance by tuning Cr redox properties. 125,126 Therefore, compatibility between dehydrogenation and metathesis catalysts (i.e., formation of secondary phases) and anchoring over a suitable support, is another field that to the best of our knowledge has been unexplored so far and is important to study, especially when considering different catalyst contact states in the reactor. The parameters involved prevent us from establishing an overall ''compatibility table'', as this will depend on all the previously discussed factors.…”

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] .…”

“…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] . 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 [16, 19, 20] …”

“…[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. [16,19,20] Porous single-crystalline transition-metal nitride monoliths combining the ordered lattice structures and disordered interconnected pores would create well-defined surface structures. [21] The single-crystalline property of the monoliths therefore delivers higher stability similar to bulk single crystals and higher activity similar to nanocrystals in catalysis.…”

“…[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.…”