The team’s starting material was a catalyst the group and others had already explored for synergistic pollutant removal: iron vanadate, FeVO4, dispersed on a titanium dioxide support. This combination is attractive because the vanadium and iron centers can drive both the selective catalytic reduction of NOx with ammonia and the oxidation of VOCs such as toluene, the two reactions that define simultaneous abatement. In laboratory settings, FeVO4/TiO2 performs admirably. But industrial environments are unforgiving. Alkali metals like potassium, released from coal and biomass combustion, and heavy metals like lead, volatilized in sintering plants and waste incinerators, drift onto catalyst surfaces and gradually strangle their activity. A catalyst that works beautifully on a clean feed but dies within months on a real flue gas is of limited practical value.

To quantify that threat, the researchers deliberately exposed their catalysts to potassium and lead species and measured how NO conversion and toluene oxidation responded. The results painted a nuanced picture. Potassium proved to be the more insidious enemy: it aggregated on the catalyst surface, blocking the acidic sites where ammonia must adsorb before it can reduce NOx, and directly poisoning the active sites responsible for the reaction. Lead, by contrast, turned out to be a surprisingly gentle adversary for this particular system. The unmodified FeVO4/TiO2 catalyst showed an intrinsic tolerance to lead, suffering only minor inhibition of NO conversion while actually exhibiting enhanced toluene oxidation, an intriguing case where the poison partially acted as a promoter rather than a killer.

The most sobering finding, however, came when both poisons were present at once. Simultaneous potassium and lead exposure caused far more severe deactivation than either element alone, revealing a synergistic poisoning effect in which the two contaminants compound each other’s damage. This observation matters because real flue gas never delivers its toxins one at a time. Any catalyst destined for industrial service must be evaluated against mixed-poison scenarios, and the study’s demonstration that combined K and Pb exposure is worse than the sum of its parts offers a warning to the field: single-poison laboratory tests may dramatically underestimate the degradation a catalyst will experience in the field.

The researchers’ countermeasure was molybdenum. By doping Mo into the FeVO4/TiO2 framework, they fundamentally changed how the catalyst responds to potassium attack. Spectroscopic and performance analyses showed that Mo modification alleviated the K-induced blockage of acid sites and the poisoning of active sites by suppressing the aggregation of potassium across the catalyst surface. Instead of potassium clustering into deactivating islands, it was held in a more dispersed, less damaging state. This anti-poisoning mechanism builds on a growing body of evidence that molybdenum addition can harden vanadia-based selective catalytic reduction catalysts against alkali metals, and the new work extends that strategy to the dual-function NOx-plus-VOCs setting.

Molybdenum did more than play defense. The doped catalyst also gained offensive advantages that boosted its baseline performance. Mo addition stabilized the high-valence V5+ and Fe3+ species, the redox workhorses that shuttle electrons during both the ammonia-SCR reaction and the oxidation of toluene, and it preserved an abundance of oxygen vacancies on the surface. Oxygen vacancies are critical in oxidation catalysis because they activate molecular oxygen and facilitate the Mars-van-Krevelen cycle through which lattice oxygen participates in breaking carbon-hydrogen bonds in VOC molecules. By keeping more of the vanadium and iron in their catalytically potent oxidation states and maintaining a vacancy-rich surface, the Mo-doped catalyst sustained the redox chemistry that underpins both pollutant-removal reactions.

The structural benefits extended to the pore network as well. Molybdenum incorporation improved the catalyst’s pore structure, providing more acid sites overall and promoting a more uniform and stable distribution of those sites across the surface. In an ammonia-SCR catalyst, acid sites are where the NH3 reagent adsorbs and is activated before reacting with NOx, so their quantity and accessibility directly govern NO conversion. A more even distribution means that incoming poisons cannot wipe out entire neighborhoods of activity in one strike, and a larger population of sites provides redundancy. Together with the stabilized redox species and the suppressed potassium migration, these effects explain why the Mo-doped catalyst retained its dual-function performance under poisoning conditions that crippled the undoped material.

The broader significance of the work lies in its design philosophy. Rather than chasing record activity numbers on clean feeds, the researchers treated poisoning resistance as a first-order design criterion, systematically evaluating deactivation mechanisms and engineering the catalyst to counter them. Their conclusions offer a theoretical foundation and a practical strategy for developing simultaneous NOx and VOCs removal catalysts with enhanced resistance to K and Pb poisoning. The approach, stabilizing high-valence active species, preserving oxygen vacancies, enriching and homogenizing acid sites, and physically frustrating the aggregation of alkali poisons, is modular and could plausibly be transferred to other catalyst families, including the ceria- and manganese-based systems that many groups are developing for low-temperature applications.

There remain hurdles between laboratory demonstration and industrial deployment. The durability of any catalyst must ultimately be proven over thousands of hours in genuine flue gas, where sulfur dioxide, water vapor, particulate matter, and temperature excursions add further stresses beyond the potassium and lead examined here. Regeneration protocols, mechanical strength, and manufacturing cost will also shape whether Mo-doped FeVO4/TiO2 ever lines the ducts of a working power plant. Yet the study delivers something the field genuinely needs: a mechanistically grounded account of how two common industrial poisons interact with a dual-function catalyst, and a demonstrated doping strategy that blunts their combined assault. As regulators tighten limits on both NOx and VOC emissions, and as industries from steel sintering to waste incineration seek compact end-of-pipe solutions, catalysts that can fight two pollutants at once and keep fighting through the poison will be in growing demand. This work shows that a single well-chosen dopant can tip the balance.

Subject of Research: Mo-doped FeVO4/TiO2 catalysts for simultaneous NOx and VOCs removal with enhanced resistance to potassium and lead poisoning

Article Title: Mo-doped FeVO4/TiO2 catalysts with abundant acidic sites for simultaneous NOx and VOCs abatement: enhanced resistance to K and Pb poisoning

Article References: Wu, Y.-W., Su, X., Li, X.-H., Xu, S., Wu, Z.-L., Zhou, X.-Y., Li, J.-H., & Lu, Q. (2026). Mo-doped FeVO4/TiO2 catalysts with abundant acidic sites for simultaneous NOx and VOCs abatement: enhanced resistance to K and Pb poisoning. Journal of Materials Science. https://doi.org/10.1007/s10853-026-13896-1

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13896-1

Keywords: catalysis, NOx removal, VOCs oxidation, NH3-SCR, molybdenum doping, FeVO4/TiO2, potassium poisoning, lead poisoning, flue gas treatment, oxygen vacancies, acid sites, air pollution control

The research, led by Deok Woo Kim, Dong Seop Choi, and Ji Bong Joo of Konkuk University’s Department of Chemical Engineering, tackles a long-standing dilemma in catalyst design. The standard method for opening up zeolites, known as desilication, involves treating the crystals with an alkaline solution such as sodium hydroxide. The alkali selectively dissolves silicon species from the framework, carving out larger pores that improve access. But the process is destructive and difficult to control. As silica dissolves, it can reprecipitate randomly as amorphous deposits on the crystal surface, blocking the very openings the treatment was meant to create. Worse, prolonged alkali exposure can collapse the zeolite framework entirely, destroying the microporosity and acid sites that give the material its catalytic power in the first place.

The Korean team’s solution was to introduce a surfactant, cetyltrimethylammonium bromide or CTAB, into the synthesis. Their procedure began by stirring ZSM-5 zeolite with a sodium hydroxide solution at room temperature, then adding a CTAB solution and transferring the mixture to a Teflon-lined autoclave for hydrothermal treatment at 130 degrees Celsius. After adjusting the pH to approximately 8 and continuing treatment for another 24 hours, the product was filtered, dried, and calcined at 550 degrees Celsius to burn away the organic template. The resulting material, designated HF_ZSM-5, was compared against a conventional alkali-treated sample, AT_ZSM-5, prepared by simply stirring ZSM-5 in a 0.5 molar sodium hydroxide solution at 80 degrees Celsius for five hours.

The characterization results reveal why the surfactant approach is so effective. X-ray diffraction confirmed that all samples retained the characteristic ZSM-5 framework, but the alkali-treated material showed markedly reduced crystallinity, evidence of structural damage from the harsh alkaline conditions. The hierarchical material, by contrast, preserved much higher crystallinity despite facing even harsher synthesis conditions. The researchers attribute this protection to CTAB micelles that electrostatically bind to the negatively charged zeolite surface, acting as a shield against excessive silica dissolution. Strikingly, the hierarchical sample also displayed new low-angle diffraction peaks near 2.3, 4.2, and 4.8 degrees, the signature of long-range ordered hexagonal mesoporous aluminosilicate resembling the well-known material MCM-41. In other words, the treatment did not merely etch holes in the crystal; it grew an entirely new ordered mesoporous phase on its surface.

Nitrogen adsorption measurements told a complementary story. Pristine ZSM-5 showed the classic type I isotherm of a purely microporous material. The alkali-treated sample shifted toward a type IV isotherm, indicating mesoporosity, and adsorbed far more nitrogen overall, yet paradoxically exhibited the lowest specific surface area of all the samples. This apparent contradiction points to severe framework damage: excessive alkali treatment had collapsed the micropore structure, destroying the internal surface area even as it created larger voids. The hierarchical zeolite, meanwhile, maintained a surface area comparable to the pristine material while simultaneously developing a clear distribution of mesopores in the 1 to 10 nanometer range. Transmission electron microscopy provided direct visual confirmation, revealing cylindrical pores arranged in hexagonal arrays on the surface of the hierarchical crystals, while the alkali-treated sample showed only cracks and disordered dissolution.

Acidity measurements using ammonia temperature-programmed desorption added another layer of insight. All treated samples lost some acid sites compared with pristine ZSM-5, an expected consequence of partial framework decomposition. Strong Brønsted acid sites, associated with the higher-temperature desorption peak near 400 degrees Celsius, declined more steeply than weak sites, suggesting that desilication converts strong sites into weaker ones, possibly as silica-free alumina surfaces that function as external acid sites. Crucially, the hierarchical material preserved its strong acid sites better than the simply alkali-treated sample, again because the CTAB micelles blocked deep penetration of alkaline species into the framework. The newly formed mesoporous aluminosilicate layer also contributed additional acid sites of its own, similar to those found in aluminum-containing MCM-41.

The catalytic payoff came in cracking tests conducted in a fixed-bed reactor at 500 degrees Celsius. The team chose 1,3,5-triisopropylbenzene, or TIPB, as a probe molecule for bulky feedstocks. At 0.95 nanometers, TIPB is far too large to enter the micropores of ZSM-5, so pristine zeolite could only crack it slowly on its limited external surface, achieving a conversion of just 40.1 percent. The alkali-treated sample performed better by opening access to exposed acid sites. But the hierarchical zeolite was the clear winner, reaching 80.8 percent conversion, exactly 2.01 times higher than the pristine material. Product selectivity reinforced the conclusion: the hierarchical catalyst showed the greatest selectivity toward benzene, the deep-cracking product, indicating that molecules were diffusing through the mesopores and undergoing extensive catalytic cracking rather than simple thermal pyrolysis.

A second test with n-dodecane, a linear hydrocarbon small enough to diffuse into ZSM-5 micropores, revealed a different but equally important advantage. Here the pristine zeolite achieved the highest conversion thanks to its abundant internal acid sites, while the alkali-treated sample fared worst because its collapsed framework had lost so much acidity. The hierarchical material landed in between, retaining enough acid sites for respectable conversion. The decisive metric, however, was coke formation. Coke, the polyaromatic carbonaceous residue that builds up when cracked hydrocarbon fragments linger and carbonize inside pores, is the chief cause of catalyst deactivation in industrial cracking. Pristine ZSM-5, despite its high conversion, produced the most coke because its strong acid sites trap intermediates within narrow micropores. The hierarchical zeolite produced the least coke of all, because its mesopore network allowed fragments to diffuse out before they could accumulate and transform into pore-blocking polyaromatics.

The implications for the petroleum industry are considerable. Fluid catalytic cracking remains the dominant route to transportation fuels worldwide, and its efficiency hinges on how well catalysts can convert the heaviest, bulkiest fractions of crude oil. The Konkuk team’s findings demonstrate that surfactant-templated recrystallization can deliver the best of both worlds: a preserved crystalline zeolite framework with its strong acid sites intact, plus an ordered network of mesopores that welcomes large molecules and sweeps coke precursors away. Compared with conventional desilication, which trades structural integrity for porosity, the hierarchical approach achieved higher conversion of bulky molecules, retained substantial activity toward smaller ones, and minimized deactivating coke deposits. As refineries face pressure to process heavier feedstocks and squeeze more value from every barrel, catalysts engineered with this kind of hierarchical pore architecture could prove transformative, turning molecular traffic jams into open highways for chemistry.

Subject of Research: Synthesis of hierarchical mesoporous zeolites for enhanced catalytic cracking of bulky hydrocarbon molecules

Article Title: Synthesis of hierarchical zeolites for enhanced catalytic cracking performance toward larger hydrocarbon molecules

Article References: Kim, D. W., Choi, D. S., & Joo, J. B. (2025). Synthesis of hierarchical zeolites for enhanced catalytic cracking performance toward larger hydrocarbon molecules. Advances in Industrial and Engineering Chemistry, 1(1), Article 30. https://doi.org/10.1007/s44405-025-00031-y

Image Credits: AI Generated

DOI: 10.1007/s44405-025-00031-y

Keywords: zeolites, hierarchical zeolites, catalytic cracking, ZSM-5, mesoporous materials, fluid catalytic cracking, desilication, CTAB surfactant, MCM-41, coke formation, acid sites, petroleum refining