The isomerization of glucose to fructose is an important step in the conversion of biomass to valuable fuels and chemicals. A key challenge for the isomerization reaction is achieving high selectivity towards fructose using recyclable and inexpensive catalysts. Imogolite is a singlewalled aluminosilicate nanotube characterized by surface areas of 200-400 m 2 /g and pore widths near 1 nm. In this study, imogolite nanotubes are used as a heterogeneous catalyst for the isomerization of glucose to fructose. Catalytic testing demonstrates the catalytic activity of imogolite for the isomerization of glucose to fructose. Imogolite is a highly tunable structure and can be modified through substitution of Si with Ge or through functionalization of methyl groups to the inner surface. These modifications change the surface properties of the nanotubes and enable tuning of the catalytic performance. Aluminosilicate imogolite is the most active material for the conversion of glucose. Conversion of glucose of 30% and selectivity for fructose of 45% is achieved using aluminosilicate imogolite. Modification of imogolite with germanium or methyl groups decreases the conversion, but increases the selectivity. Generally, the selectivity for fructose decreases as the conversion of glucose increases. Interestingly, the imogolite nanotubes have comparable catalytic selectivity at similar conversion as base catalyzed reactions. Catalyst recycling experiments revealed that organic content accumulates on the nanotubes that results in a minor reduction in conversion while maintaining similar catalytic selectivity. Overall, imogolite nanotubes demonstrate an active and tunable catalytic platform for the isomerization of glucose to fructose.

High-porosity yttria-and ytterbia-stabilized zirconia aerogels offer the potential of extremely low thermal conductivity materials for high-temperature applications. Yttria-and ytterbia-doped zirconia aerogels were synthesized using a sol-gel approach over the dopant range of 0-20 atomic percent. Surface area, pore volume, and morphology of the as-dried aerogels and materials thermally exposed for short periods of time to temperatures up to 1200°C were characterized by nitrogen physisorption, scanning and transmission electron microscopy, and X-ray diffraction. The aerogels as supercritically dried all were X-ray amorphous. At a 5% dopant level, a tetragonal structure with a smaller monoclinic phase developed on thermal exposure. Mixed tetragonal and cubic phases or predominantly cubic materials were observed at higher dopant levels, depending on the dopant level, temperature and exposure time. The formation of crystalline phases was accompanied by loss of surface area and pore volume, although some mesoporous structure was maintained on short-term exposure to 1000°C. Incorporation of the smaller Yb atom into the lattice structure resulted in smaller lattice dimensions on crystallization than was seen with Y doping and favored a more highly equiaxed structure. Aerogels synthesized with 15% Y maintained the smallest particle size without evidence of sintering at 1100°C.

A significant challenge in the field of aerospace materials is the development of lightweight, highly insulating materials that can survive in extreme environments. Materials with reduced thermal conductivity permit higher operating temperatures and improved insulative performance. Reduced weight mitigates cost and improves payload capacity. A promising class of lightweight, low thermal conductivity materials are aerogels. Aerogels are highly porous, extremely lightweight, and display extraordinarily low thermal conductivity. 1 The same highly porous structure is also the source of a critical engineering challenge: thermal stability. Upon thermal exposure, the aerogel's highly porous structure collapses, and the favorable properties of low thermal conductivity and low density are diminished. Aerogels with improved thermal stability must be developed to enable the use of aerogels as insulation in extreme environments and temperatures to 1200°C.Polymeric aerogels, which demonstrate excellent mechanical properties, are limited to temperatures below 500°C due to the polymer network's decomposition. 2,3 Silica aerogels, perhaps the most studied and well-known, undergo significant sintering and densification above 700°C. [4][5][6] Exploration of various metal oxides have led to mixed results. Zirconia aerogels lose much of their specific surface area (SSA) upon heating, from 282 m 2 /g as dried to

The high porosities and low densities of ceramic aerogels offer outstanding insulative performance in applications where weight is a critical factor. The high surface area‐to‐volume ratios and specific surface areas provide extremely low thermal conductivity, but also contribute to rapid densification of the pore structure at elevated temperatures. This densification diminishes their favorable properties and inhibits use of aerogels in high temperature applications. This work contributes to a design framework for thermally stable aerogels via the study of dopant chemistry (Y, Yb, Gd, Ca, Ce) in zirconia aerogels. The structural evolution was studied to 1200°C using nitrogen physisorption, scanning electron microscopy, and x‐ray diffraction. The role of dopant identity and concentration in thermal stability was elucidated. In context of the design framework, dopant chemistry is an aggregate for many closely related material properties, each of which may contribute to aerogel structural evolution. To develop a truly predictive design framework for ceramic‐based aerogels, systematic and comprehensive evaluation of thermodynamic and kinetic properties must be performed in conjunction with studies on structural evolution.This article is protected by copyright. All rights reserved