(521cb) Engineering Zeolite Catalysts with Tunable Boron Active Sitesfor Oxidative Dehydrogenation of Propane
AIChE Annual Meeting
2023
2023 AIChE Annual Meeting
Catalysis and Reaction Engineering Division
Poster Session: Catalysis and Reaction Engineering (CRE) Division
Wednesday, November 8, 2023 - 3:30pm to 5:00pm
Oxygen-assisted oxidative dehydrogenation of propane (ODHP) is a promising technology to
produce propylene from shale gas could bridge the gap between continuously growing market
and productivity; however, overoxidation of propane to COx is the main challenge on traditional
metal oxide catalysts. Prior studies have shown that boron nitride can achieve ca. 90% light
olefins selectivity at 14% propane conversion, thus demonstrating the potential for using boron-
based catalysts in ODHP reactions. Here, we discuss methods of synthesizing zeolites catalysts
with different active site speciation as a means of developing structure-performance relationships
for ODHP. The substitution of Si and Al sites with various heteroatoms, such as boron, has been
a subject of increased interest owing to the ability to tailor zeolite acidity and also to explore
tandem catalysts with distinct, cooperative active sites. It has been shown that boron-containing
MFI-type zeolites are active catalysts for ODHP, capable of achieving ca. 80% light olefins
selectivity at 40% propane conversion. Despite studies of B-zeolites in the literature, the
temporal changes in boron speciation and the role of each site in the ODHP reaction mechanism
remain elusive. To this end, we have synthesized a series of B-zeolites using the small-pore
structure CHA (chabazite), which is more shape-selective for lighter olefins than medium-pore
zeolites (e.g. MFI). Using 11 B solid-state NMR spectroscopy to characterize different boron
species in CHA, we showed that the relative percentages of framework B[4], B[3], and defect
(B(OSi) x OH 3-x(x=1,2) ) sites can be controlled. We will discuss how different boron-containing CHA
zeolites with varying percentages of defects and adjacent Si-OH groups impact catalyst activity;
and how reaction conditions impact the time-resolved distribution of active site speciation.
produce propylene from shale gas could bridge the gap between continuously growing market
and productivity; however, overoxidation of propane to COx is the main challenge on traditional
metal oxide catalysts. Prior studies have shown that boron nitride can achieve ca. 90% light
olefins selectivity at 14% propane conversion, thus demonstrating the potential for using boron-
based catalysts in ODHP reactions. Here, we discuss methods of synthesizing zeolites catalysts
with different active site speciation as a means of developing structure-performance relationships
for ODHP. The substitution of Si and Al sites with various heteroatoms, such as boron, has been
a subject of increased interest owing to the ability to tailor zeolite acidity and also to explore
tandem catalysts with distinct, cooperative active sites. It has been shown that boron-containing
MFI-type zeolites are active catalysts for ODHP, capable of achieving ca. 80% light olefins
selectivity at 40% propane conversion. Despite studies of B-zeolites in the literature, the
temporal changes in boron speciation and the role of each site in the ODHP reaction mechanism
remain elusive. To this end, we have synthesized a series of B-zeolites using the small-pore
structure CHA (chabazite), which is more shape-selective for lighter olefins than medium-pore
zeolites (e.g. MFI). Using 11 B solid-state NMR spectroscopy to characterize different boron
species in CHA, we showed that the relative percentages of framework B[4], B[3], and defect
(B(OSi) x OH 3-x(x=1,2) ) sites can be controlled. We will discuss how different boron-containing CHA
zeolites with varying percentages of defects and adjacent Si-OH groups impact catalyst activity;
and how reaction conditions impact the time-resolved distribution of active site speciation.