The separation of Pd and CeO₂ on the inner surface of controlled porous glass (CPG, obtained from phase-separated borosilicate glass after extraction) yields long-term stable and highly active methane combustion catalysts. However, the limited availability of the CPG makes such catalysts highly expensive and limits their applicability. In this work, porous silica obtained from acid leached rice husks after calcination (RHS) was used as a sustainable, cheap and broadly available substitute for the above mentioned CPG. RHS-supported Pd-CeO₂ with separated CeO₂ clusters and Pd nanoparticles was fabricated via subsequent impregnation/calcination of molten cerium nitrate and different amounts of palladium nitrate solution. The Pd/CeO₂/RHS catalysts were employed for the catalytic methane combustion in the temperature range of 150–500 °C under methane lean conditions (1000 ppm) in a simulated off-gas consisting of 9.0 vol% O₂, and 5.5 vol% CO₂ balanced with N₂. Additionally, tests with 10.5 vol% H₂O as co-feed were carried out. The results revealed that the RHS-supported catalysts reached the performance of the cost intensive benchmark catalyst based on CPG. The incorporation of Pd-CeO₂ into RHS additionally improved water-resistance compared to solely Pd/CeO₂ lowering the required temperature for methane combustion in presence of 10.5 vol% H₂O to values significantly below 500 °C (T₉₀ = 425 °C).

A thermo-chemical treatment method was used to produce biogenic amorphous silica from South African sugarcane and maize residues. Different fractions of South African sugarcane (leaves, pith, and fiber) were processed for silica production. The biomass samples were leached with either 7 wt% citric acid or 7 wt% sulfuric acid at 353 K for 2 h prior to being rinsed, dried and combusted using a four-step program ranging from room temperature to 873 K in a furnace. The characterization of the pre-treated biomass samples was conducted using thermogravimetric analysis (TG/DTA), X-ray fluorescence analysis (XRF) and elemental analysis (CHN), while the final products were characterized by XRF, X-ray diffraction (XRD), elemental analysis, nitrogen physisorption and scanning electron microscopy (SEM). Citric acid pre-treatment proved to be an attractive alternative to mineral acids. Amorphous biogenic silica was produced from sugarcane leaves in good quality (0.1 wt% residual carbon and up to 99.3 wt% silica content). The produced biogenic silica also had great textural properties such as a surface area of up to 323 m² g⁻¹, average pore diameter of 5.0 nm, and a pore volume of 0.41 cm³ g⁻¹.

Pre-shaped mesoporous amorphous rice husk ash (RHA) and MCM-41 derived from RHA as a silica source were transformed into MFI-type zeolites using two different structure-directing agents. Tetrapropylammonium hydroxide (TPAOH) was utilized as an alkali source for silica dissolution and structure control during the direct transformation of RHA into zeolite. A monopropylamine (PA)-containing alkaline solution (NaOH) was used for the pseudomorphic transformation of RHA or MCM-41 into zeolite. The hydrothermal conversion of RHA or MCM-41 into MFI-type zeolites was investigated as a function of reaction time at 175 °C. With PA as template, the crystallization took place inside and on the outer surface of RHA or MCM-41 without losing the original shape of the initial silica sources, while TPAOH led to the formation of conventional MFI-type zeolite crystals due to the complete dissolution of RHA. The final products were characterized by X-ray diffraction, nitrogen adsorption, scanning electron microscopy, and optical emission spectroscopy.

This work introduces a cost and time efficient procedure to specifically increase mesopore volume and specific surface area of biogenic silica (specific surface area: 147 m² g⁻¹ and mesopore volume: 0.23 cm³ g⁻¹) to make it suitable for applications in adsorption or as catalyst support. The target values were a specific surface area of ~500 m² g⁻¹ and a mesopore volume of ~0.40–0.50 cm³ g⁻¹ as these values are industrially relevant and are reached by potential concurring products such as precipitated silica, silica gel, and fumed silica. The applied process of partial pseudomorphic transformation was carried out as a single reaction step in a microwave reactor instead of commonly used convective heating. In addition, the conventionally used surfactant cetyltrimethylammonium bromide (CTABr) was substituted by the low-cost surfactant (Arquad^® 16-29, cetyltrimethylammonium chloride (CTACl) aqueous solution). The influence of microwave heating, type of surfactant as well as the concentration of NaOH and CTACl on the textural and structural properties of the modified biogenic silica was investigated using nitrogen adsorption as well as scanning and transmission electron microscopy. The results show that the textural parameters of the modified biogenic silica can be exactly controlled by the amount of NaOH in the reaction solution. By variation of the NaOH concentration, specific surface areas in the range of 215–1,001 m² g⁻¹ and mesopore volumes of 0.25–0.56 cm³ g⁻¹ were achieved after reaction at 393 K for 10 min. The presented microwave route using the low-cost surfactant solution decreases the reaction time by 99% and as shown in an example for German prices, lowers the costs for the surfactant by 76–99%.