Biomass gasification is a promising pathway for sustainable hydrogen production, leveraging renewable feedstocks such as agricultural residues, forestry waste, and energy crops. A critical challenge in this process is optimizing hydrogen yield while minimizing tar formation, which can clog systems and reduce efficiency. Advanced catalysts play a pivotal role in addressing these challenges, with nickel-based materials, dolomite, and olivine being widely studied for their catalytic properties. Recent developments in nanocatalysts and bifunctional materials further enhance performance, though deactivation mechanisms like coking and sintering remain key obstacles.

Nickel-based catalysts are the most extensively researched due to their high activity in tar reforming and hydrogen production. These catalysts typically consist of nickel supported on alumina, silica, or other oxides, which provide structural stability. The nickel active sites facilitate steam reforming and water-gas shift reactions, converting tars and methane into hydrogen and carbon monoxide. Experimental studies show that nickel catalysts can achieve hydrogen yields exceeding 60% by volume under optimal conditions. However, their susceptibility to coking—where carbon deposits block active sites—limits long-term stability. Sulfur poisoning from biomass feedstocks also deactivates nickel catalysts, necessitating robust feedstock pretreatment or sulfur-resistant formulations.

Dolomite, a calcium-magnesium carbonate mineral, is a cost-effective alternative, particularly for in-bed tar reduction. Its primary mechanism involves cracking heavy hydrocarbons into lighter gases while promoting char gasification. Dolomite’s alkaline nature enhances water-gas reactions, increasing hydrogen output. Unlike nickel catalysts, dolomite is less prone to coking but suffers from attrition and fragmentation in fluidized bed reactors, requiring frequent replenishment. Calcined dolomite, produced by heating to remove carbonates, exhibits higher porosity and reactivity, with studies reporting tar reductions of up to 90% in some configurations.

Olivine, a magnesium-iron silicate, shares similarities with dolomite but offers superior mechanical strength, making it suitable for high-temperature applications. Its iron content provides redox activity, aiding tar decomposition. While olivine is less active than nickel, its durability and resistance to attrition make it a practical choice for continuous operations. Modified olivine, doped with nickel or other transition metals, bridges the gap between activity and stability, with experimental data showing a 40–50% improvement in hydrogen yield compared to untreated olivine.

Catalyst deactivation is a major hurdle in biomass gasification. Coking occurs when carbonaceous species polymerize on catalyst surfaces, blocking active sites. Sintering, the agglomeration of metal particles at high temperatures, reduces surface area and activity. Sulfur and chlorine compounds in biomass can permanently poison catalysts by forming stable sulfides or chlorides. To mitigate these issues, researchers employ strategies such as steam injection to gasify carbon deposits, periodic oxidative regeneration to burn off coke, and alloying nickel with metals like cobalt or copper to improve resistance.

Regeneration methods vary by catalyst type. Nickel catalysts can often be restored through controlled oxidation followed by reduction, though repeated cycles degrade performance over time. Dolomite and olivine, being minerals, are typically replaced rather than regenerated due to their low cost, though some studies explore thermal reactivation for dolomite. Emerging techniques like microwave-assisted regeneration show promise for reducing energy input and processing time.

Recent advancements focus on nanocatalysts and bifunctional materials to overcome limitations. Nickel nanoparticles dispersed on high-surface-area supports like cerium oxide or zirconia exhibit enhanced activity and coke resistance due to improved metal-support interactions. Bifunctional catalysts combine acidic and basic sites to simultaneously crack tars and reform light gases, with experimental results demonstrating hydrogen yields surpassing 70%. Perovskite-type oxides and spinels are also gaining attention for their thermal stability and tunable redox properties.

Nanostructured catalysts, such as core-shell designs, protect active sites from deactivation while maintaining high reactivity. For example, a nickel core encapsulated in a porous silica shell reduces sintering and coking while allowing reactant diffusion. Similarly, bimetallic nanoparticles (e.g., Ni-Fe) show synergistic effects, improving both activity and durability. Lab-scale tests indicate that these advanced materials can reduce tar content to below 50 mg/Nm³, meeting stringent system requirements.

Despite these innovations, scalability and cost remain barriers. Nanocatalysts often involve complex synthesis routes, such as sol-gel or chemical vapor deposition, which are expensive at industrial scales. Bifunctional materials require precise control over composition and structure, complicating large-scale production. Ongoing research aims to simplify manufacturing and improve catalyst lifetimes to make these solutions economically viable.

In summary, advanced catalysts are indispensable for efficient biomass gasification, balancing hydrogen production and tar management. Nickel-based systems dominate in activity but face deactivation challenges, while dolomite and olivine offer robustness at the expense of lower performance. Emerging nanomaterials and bifunctional designs push the boundaries of efficiency but require further development for widespread adoption. As biomass gasification evolves, catalyst innovation will remain central to unlocking its potential for clean hydrogen production.