NOVELTY - An adsorbent catalytic nanoparticle (N1) comprises: at least one adsorbent functional group; and at least one catalytic material.    USE - AS an adsorbent catalytic nanoparticle for catalyzing chemical transformation of the fatty acid, fatty acid ester and a triglyceride (claimed); for selectively removing fatty acids from feedstocks for biodiesel, and hydrotreating the separated fatty acids.    ADVANTAGE - The adsorbent catalytic nanoparticle can be used to selectively remove fatty acids from feedstocks for biodiesel, and to conveniently hydrotreat the separated fatty acids. The adsorbent catalytic nanoparticle catalyzes decarboxylation and hydrodeoxygenation of a free fatty acid at a higher rate than a mesoporous nanoparticle not having the adsorbent functional group bound to it. The adsorbent catalytic nanoparticle catalyzes cracking of a free fatty acid at a lower rate than a corresponding mesoporous silica nanoparticle not having the adsorbent functional group bound to it.    DETAILED DESCRIPTION - An adsorbent catalytic nanoparticle (N1) comprises: at least one adsorbent functional group selected from amino(1-20C alkyl), 1-20C alkyl carboxylic acid, 1-20C alkyl sulfonic acid, perfluoro(1-20C alkyl) and their salt, where the alkyl unit of the aminoalkyl, alkyl carboxylic acid, alkyl sulfonic acid, and perfluoroalkyl group is covalently bound to a mesoporous silica nanoparticle, and where the 1-20C alkyl groups of the amino(1-20C alkyl) group are optionally interrupted by one or two -NH- groups; and at least one catalytic material. INDEPENDENT CLAIMS are included for the following:    (1) a method (M1) involving: combining at least one adsorbent catalytic nanoparticle (N1) with at least one first molecule that is selectively adsorbed by the adsorbent functional group, to provide a mixture;    (2) a method involving: combining at least one adsorbent catalytic nanoparticle (N1) with a free fatty acid, to provide a mixture; and combining the mixture with hydrogen gas under conditions so that the catalytic material at least one of cracks, decarboxylates, and hydrodeoxygenates at least some of the free fatty acid; and    (3) a method involving: combining at least one adsorbent catalytic nanoparticle (N1) with a solution comprising a free fatty acid and at least one of a fatty acid ester and a triglyceride, to provide a mixture; separating the adsorbent catalytic nanoparticle having the first molecule adsorbed to it from the mixture; and combining the separated adsorbent catalytic nanoparticle with hydrogen gas so that the catalytic material in the adsorbent catalytic nanoparticle catalyzes a chemical transformation of the fatty acid comprising at least one of cracking, decarboxylation, and hydrodeoxygenation.