Pseudo Boehmite For Fcc Catalyst Gel — What It Actually Is (And What It Is Not)

If you make, sell, or specify FCC catalyst, pseudo boehmite is the single largest non-zeolite raw material in your slurry tank. The decision between gel and spray-dried powder is not just a logistics question: a 30% swing in microsphere attrition index can come from this choice alone. This guide explains what pseudo boehmite is at the molecular level, how it is made, and how gel-vs-powder differences propagate into the FCC microsphere properties your refinery actually measures.

Fluid catalytic cracking (FCC) is the heart of every modern refinery. The catalyst itself is a 60 to 75 micron microsphere composed of three components: an active zeolite (typically USY or ZSM-5), a matrix clay (kaolin), and a binder. The binder holds everything together mechanically, provides most of the catalyst's macroporosity, and is the medium through which reactant molecules diffuse to the zeolite crystals. For more than nine out of ten commercial FCC catalysts, that binder is pseudo boehmite.

The reason is a single physical property: pseudo boehmite peptizes. When stirred with dilute nitric or hydrochloric acid, it converts almost completely into a transparent, low-viscosity colloidal alumina sol. The sol coats the zeolite and clay particles, and during spray drying it glues them into a mechanically robust microsphere. True boehmite (well-crystallized) does not peptize. Gibbsite (Al(OH)3) does not peptize. Bayerite does not peptize. Only the poorly crystallized, high-surface-area form between gibbsite and boehmite — pseudo boehmite — has the right combination of reactivity, surface area, and cost to serve as the FCC binder.

The next sections walk through the molecular structure, the industrial manufacturing routes, the gel-vs-powder property differences, and the quantitative impact on FCC catalyst performance. By the end you should be able to read a pseudo boehmite Certificate of Analysis and know exactly which grade matches your FCC application.

Pseudo boehmite has the nominal chemical formula AlOOH·nH2O, where n typically runs between 0.08 and 0.62 depending on aging and drying. The structure is the same orthorhombic gamma-AlOOH as true boehmite, but with two important differences: the crystallite size is much smaller (3 to 10 nm instead of 30 to 100 nm), and a large amount of interlayer water is incorporated into the structure. This combination gives pseudo boehmite its very high surface area (180 to 320 m2/g versus below 20 m2/g for true boehmite) and its ability to peptize in acid.

The boehmite layer is built from edge-sharing AlO6 octahedra. In true boehmite these layers stack in an ordered, hydrogen-bonded fashion with very little water between them. In pseudo boehmite the layers are smaller, more turbostratic, and trap 1.5 to 2.5 layers of water molecules in the interlayer gap. This water is what makes pseudo boehmite reactive: when acid is added, protons exchange with the interlayer water and the layers exfoliate into individual nanocrystallites, forming a stable colloidal sol.

Pseudo Boehmite For Fcc Catalyst Gel — The Hidden Defect / Failure Mode

The aluminum hydroxide family includes gibbsite (Al(OH)3, also called hydrargillite), bayerite (alpha-Al(OH)3), nordstrandite, and the oxyhydroxide family includes boehmite (gamma-AlOOH) and diaspore (alpha-AlOOH). Pseudo boehmite is the disordered, low-crystallinity form of boehmite. In X-ray diffraction it shows only two broad peaks (around 2-theta = 14.5 and 38.4 degrees) instead of the four sharp peaks of true boehmite. This is the simplest analytical test: if your sample's XRD pattern shows sharp boehmite peaks, it is true boehmite and will not work as an FCC binder.

The peptization row in this table is the key. The other three materials either do not react with acid at all (gibbsite, gamma-alumina) or react so poorly that they cannot be used as a binder (true boehmite). Pseudo boehmite's combination of small crystallite size, high surface area, and disordered layer stacking makes it the unique material in the family that can be processed into a colloidal sol.

• ISO 9277:2010 — Determination of the specific surface area of solids by gas adsorption (BET method). Used to certify pseudo boehmite surface area.
• ISO 15901-1:2016 — Pore size distribution by mercury intrusion porosimetry. Used for pore volume of the calcined catalyst.
• ASTM D4222 — Standard test method for determination of nitrogen adsorption and desorption isotherms of catalysts.
• ASTM D5757 — Standard test method for determination of attrition and abrasion of FCC catalyst by air jets (the Davison Attrition Index method).
• ASTM D3906 — Standard test method for determination of relative zeolite diffraction intensity of FCC catalyst.

Pseudo Boehmite For Fcc Catalyst Gel — Measured Numbers Across Grades

Three precipitation routes dominate global pseudo boehmite production. The choice between them determines purity, residual anion, cost, and the surface-area range that can be produced. A buyer who understands the route can predict the lot-to-lot variability and the regulatory status (especially for catalyst destined for food-contact or pharmaceutical applications).

This is the highest-volume, lowest-cost route. Sodium aluminate solution (NaAlO2, typically 20 to 30 wt% Al2O3 equivalent) is reacted with aluminum sulfate solution (Al2(SO4)3, 8 to 10 wt% Al2O3) or with CO2 gas in a stirred reactor at 30 to 70 degrees C and pH 8 to 10. The product is a gel of AlOOH plus dissolved sodium sulfate. The gel is washed on a filter press or rotary vacuum filter to reduce Na2O to the specification (typically below 0.05% for FCC grade, below 0.02% for hydroprocessing). CO2 neutralization gives lower Na2O than the aluminum sulfate route and is increasingly preferred for cleaner products. Surface area is controlled by temperature, pH, and aging time: 30 degrees C and short aging give 280 to 320 m2/g; 70 degrees C and 4 to 8 hours aging give 200 to 240 m2/g.

Where Pseudo Boehmite For Fcc Catalyst Gel Earns Its Premium — Core Chemistry

Peptization index is the single most important specification. At 97% minimum (industry standard for FCC binder), the resulting FCC microsphere has Davison Attrition Index (DAI) of 1.2 to 1.8 wt%/hr. Drop peptization to 92% and the same formulation gives DAI of 3.0 to 4.5 wt%/hr. The reason: incompletely peptized boehmite particles act as unbonded inclusions in the microsphere. When the microsphere is struck in the jet-cup test or hit the cyclones in a real unit, those inclusions pop out and generate fines.

The pseudo boehmite surface area translates directly into the catalyst's matrix activity. The matrix is responsible for pre-cracking of large molecules (the so-called "bottom-of-the-barrel" conversion that protects the zeolite from pore blockage). Higher surface area means higher matrix activity but also higher coke deposition. Most FCC plants use 220 to 260 m2/g pseudo boehmite for the binder role: high enough for matrix activity, low enough to keep coke on the matrix (not the zeolite) manageable. Resid FCC units processing heavier feeds prefer 200 to 230 m2/g to limit matrix coking.

Pseudo boehmite D50 should be 30 to 50 micron for FCC binder application. Finer material (below 20 micron) peptizes too fast and gels the slurry before spray drying. Coarser material (above 80 micron) gives weak microsphere cores. The PSD width (D90/D10 ratio) also matters: tight PSD below 4 gives more uniform sol and lower AI; broad PSD above 8 gives wider AI distribution and an average 0.5 to 1.5 wt%/hr higher than tight PSD at the same D50.

Pseudo Boehmite For Fcc Catalyst Gel — Dosing Across Service Conditions

Gel has a 48 to 72 hour shelf life at room temperature. If your catalyst plant runs on a 24-hour campaign basis with daily deliveries, gel works. If you batch-produce catalyst once a week or stockpile for a month, powder is required. Most merchant catalyst manufacturers use powder with a 2 to 4 week inventory.

Pseudo boehmite gel is 75 to 82% water, so you ship 4 to 5 kg of gel for every 1 kg of Al2O3 you actually need. At a typical truck freight cost of $0.05 to $0.10 per kg per 100 km, gel freight is 3 to 4 times more expensive per kg of Al2O3 than powder. If the pseudo boehmite plant is more than 200 to 300 km from your catalyst plant, the freight savings on powder more than offset the spray-drying cost.

Hydration Kinetics, Set Control, and Working Time

The 2026 spot price of pseudo boehmite powder at 70 to 75% Al2O3 ranges from $1,200 to $2,500 per metric ton depending on grade, purity, and lot size. The biggest cost drivers, in order:

Pseudo boehmite powder for FCC is typically priced 1.3 to 1.6 times activated alumina powder on a per-ton basis (despite both being "alumina" products, the surface area and processing steps differ). Gel is priced 0.4 to 0.6 times powder on a per-ton basis, but on a per-kg-of-Al2O3 basis gel costs 2.0 to 2.5 times powder because of the 75 to 82% water content. The freight economics decide which is cheaper at the user's gate.

1. Step 1: Raw material (sodium aluminate or aluminum alkoxide): 50 to 65% of total cost. Aluminum price on the LME drives this directly.
2. Step 2: Energy for spray drying: 10 to 15% of total cost. Natural gas price is the swing factor.
3. Step 3: Washing and impurity control: 5 to 15% of total cost. Higher purity means more wash water, more filtration passes.
4. Step 4: Packing and logistics: 5 to 10% of total cost. 25 kg bags, 500 kg / 1000 kg big bags, 20 MT bulk container.
5. Step 5: QA, R&D, certification: 3 to 5% of total cost. ISO 9001, SGS audit, REACH registration.

• Form: spray-dried powder (unless integrated on the same site as the pseudo boehmite plant)
• Al2O3: 72 to 75 wt%
• Surface area (BET): 220 to 260 m2/g
• Pore volume: 0.4 to 0.6 cm3/g
• D50: 30 to 50 micron, D90/D10 below 4 (tight PSD)

Procurement Specification — What to Demand on the COA

Three trends are reshaping the pseudo boehmite market. First, the FCC catalyst industry is moving toward higher matrix activity to handle heavier feeds and higher conversion targets, which pushes demand for 260 to 320 m2/g grades with tighter PSD. Second, hydroprocessing catalyst (HDS, HDN, hydrocracking) is growing faster than FCC globally, driven by IMO 2020 and the shift to marine and rail low-sulfur fuels. This favors higher-purity Ziegler-route and CO2-neutralization pseudo boehmite. Third, lithium-ion battery separator coating is becoming a significant niche: high-purity pseudo boehmite (Na2O below 50 ppm) is used to coat PE and PP separators, improving thermal stability and electrolyte wettability. The battery-grade market is small in tonnage but high in price ($5,000 to $8,000 per ton), and is the fastest-growing pseudo boehmite segment.

For the FCC industry specifically, the trend is toward tighter PSD, higher peptization index, and lower Na2O. The "PB-Ultra" grade (Al2O3 78%+, Na2O below 0.01%, peptization 98%+) is becoming the new standard for premium FCC binder, especially for high-matrix-activity catalyst designs targeting residue feeds.

• WhatsApp: +86 133 2522 2240 (fastest, 12-hour reply)
• Email: barry@aluminaworld.com
• Sample request: 25 kg R&D pack, 7-10 day lead time, full CoA included
• Bulk orders: 1 MT MOQ, 15-20 day production, FOB/CIF/CFR from Qingdao Port (80 km from our factory)

Storage, Shelf Life, and Inventory Hygiene

Gel is the freshly precipitated, water-rich form: 18 to 25 wt% Al2O3 solids, pH 8 to 10, thixotropic paste with bulk density 0.95 to 1.10 g/cm3. It must be used within 24 to 72 hours of production because aging converts the gel toward boehmite and reduces peptization. Spray-dried powder is the same chemistry, dehydrated to 70 to 78 wt% Al2O3 (LOI 18 to 30%), bulk density 0.4 to 0.8 g/cm3, free-flowing. Powder is stable for 12 to 24 months in sealed bags. The two forms are interchangeable in finished catalyst chemistry but differ in handling: gel goes straight to the FCC slurry tank (lower cost, no re-dissolution step), powder needs re-wetting but is the only practical option for export and remote sites.

Three industrial routes dominate. (1) Sodium aluminate + aluminum sulfate (or CO2) neutralization: NaAlO2 is reacted with Al2(SO4)3 or CO2 gas at 30 to 70 degrees C and pH 8 to 10, producing a gel that is washed, filtered, and either shipped wet or spray-dried. (2) Ziegler aluminum alkoxide hydrolysis: aluminum alkoxide from Ziegler fatty alcohol synthesis is hydrolyzed with water at 60 to 90 degrees C, giving a very pure, low-soda gel; this is the premium grade used for high-purity catalyst and battery separator coating. (3) Alum (aluminum sulfate) + ammonia or sodium aluminate: cheaper but with higher residual Na2O (300 to 1000 ppm), suitable for FCC where Na2O is partly washed out downstream. The Ziegler route gives the cleanest product (Na2O below 50 ppm, SiO2 below 50 ppm) but costs 2 to 4 times more per kg of Al2O3.

• Moisture pickup in unsealed drums above 60% RH warehouse humidity (capacity loss in 30-90 days).
• Cross-contamination between activated alumina and molecular sieve stored in shared warehouses.
• Thermal-shock spalling when cold drums (-10 C winter) are opened into warm air.

• Store in sealed drums or foil-lined supersacks; re-seal immediately after partial withdrawal.
• Keep warehouse RH below 50% — climate control if you are in a tropical zone.
• If a drum has been open more than 60 days, re-test moisture and capacity before deploying into service.
• For bulk shipments above 5 t, request sealed tanker delivery with inline desiccant vent.

Total Cost of Ownership — Why Premium Pays for Itself

Both are aluminum oxyhydroxide AlOOH, but they differ in crystallinity and water content. True boehmite has the formula gamma-AlOOH with n close to 0.1, crystallite size 30 to 100 nm, well-defined XRD peaks at 2-theta = 14.5, 28.2, 38.4, and 49.3 degrees, and surface area below 20 m2/g. Pseudo boehmite has the same structure but with crystallite size of 3 to 10 nm, very broad XRD peaks (often only the 14.5 and 38.4 degree peaks are visible), high surface area (180 to 320 m2/g), and 1.5 to 2.5 layers of interlayer water (n = 0.08 to 0.62). The small crystallite size is what gives pseudo boehmite its peptization behavior. Aging in water at 60 to 100 degrees C converts pseudo boehmite to boehmite by Ostwald ripening, reducing surface area and killing peptization.

Purity is governed mainly by Fe2O3, Na2O, SiO2, and CaO residuals, plus sulfate or chloride from the precipitation chemistry. FCC catalyst binder typically uses 70 to 75% Al2O3 grade with Na2O below 0.05%, SiO2 below 0.03%, Fe2O3 below 0.02%, and SO4 below 1.0% (washed). Hydroprocessing catalyst (HDS, HDN, hydrocracking) extrudates need cleaner pseudo boehmite: Al2O3 above 75%, Na2O below 0.02%, SiO2 below 0.02%, Fe2O3 below 0.01%, SO4 below 0.5%. Three-way catalyst (TWC) washcoats and SCR washcoats need the cleanest grade: Al2O3 above 78%, Na2O below 0.01%, SiO2 below 0.01%, Fe2O3 below 0.005%, because any residual sodium poisons the platinum-group metals and the WO3/V2O5 active sites.

The math: a 5-10% longer service life plus lower thermal-cycling spalling plus reduced replacement-frequency combine to deliver 12-25% lower TCO over a single cell-stack replacement cycle, even before the safety/insurance argument for eliminating thermal-shock microcracks. The 8-15% raw-material premium pays back 1.5-2.5x over the first cycle.

Related Products & Technical Resources

We supply activated alumina, molecular sieve, and alumina-ceramic products as part of a broader specialty adsorbent catalog. The full datasheet for this grade includes additional grain-size distributions, customer-specific blend recommendations, and pilot-plant support. Talk to our technical team if your application has unusual thermal-cycling, mechanical-load, or chemical-feed constraints.

• Activated Alumina — gamma-Al2O3 adsorbent for CO2, H2S, and fluoride removal.
• Molecular Sieve — 3A / 4A / 5A / 13X grades for PSA, TSA, and drying service.
• Alumina Powder — high-purity Al2O3 powders for general industrial use.
• Aluminum Hydroxide — ATH flame retardant grade.
• Reactive Alumina Low-Soda for Castable and Burned-Magnesia Bonding
• MCFC CO2 Removal: Activated Alumina vs Carbon Molecular Sieve
• Adsorbent Bed Pressure Drop: Ergun Equation Design Guide

Next Steps — Get a Sample or Talk to Our Engineers

For samples, COAs, or application-specific blend recommendations, reach out to the Aluminaworld technical team. We hold stock of the relevant grade in our Zibo warehouse with same-week dispatch for trial orders, and we can also produce custom recipes for OEMs and EPCs with multi-ton annual demand.

Contact: WhatsApp +86 13325222240 (preferred for fast reply) or email barry@aluminaworld.com. Trial orders ship FOB Qingdao in 7-10 days; full-container shipments in 15-25 days depending on grade and customization.