Micro- and macroporous monoliths with in situ formed nickel nanoparticles were prepared for the first time by the combination of solution-based freeze casting and preceramic polymers (methyl polysiloxane). This one-step process results in macroporous monoliths composed of microporous and catalytic active nickel-containing polymer-derived ceramic. Four different complexing and cross-linking siloxanes with amino functionality were screened for their ability to create small nickel particles. TEM analysis confirmed 3-aminopropyltriethoxysilane being most efficient. High BET-specific surface areas of 344-461 m(2) g(-1) were achieved. Increased ratio of complexing groups to nickel improves the dispersion of nickel to (3.61 +/- 1.49) nm. The nickel size dependence of conversion (maximum 0.49) and CH4 selectivity (maximum 0.74) in CO2 methanation emphasizes the importance of controlling the nickel size. The hydrophobic surface characteristic is hypothesized to be the main reason polymer-derived catalysts having better catalytic activity compared with nickel-impregnated silica. The promising catalytic activity combined with the versatile freeze casting process can prospectively address heat- and mass-transfer considerations in heterogeneous monolith catalysis.