What is the origin of the names P-1 and P-2 of nickel boride catalysts? From Chapter 2 of Catalytic Hydrogenation in Organic Syntheses:


  Highly stereospecific hydrogenations of acetylenes to cis-olefins can be achieved with a nickel (P2) catalyst, prepared by sodium borohydride reduction of nickel acetate in ethanol, and ethylenediamine as a promoter.


The Wikipedia article on nickel boride describes two forms, P-1 and P-2, differing in their ratio of $\ce{Ni2B}$ to $\ce{NaBO2}$.

What is the origin of the names "P1" and "P2"? Does it have to do with whether the catalysts add hydrogen in a syn or anti fashion?
The actual differences between the two forms are well-documented on Wikipedia. As for the names: as far as I can tell, the choice of "1" and "2" seems to be arbitrary. The choice of the letter "P", though, is described by C. A. Brown (who carried out investigations into the synthesis and reactivity of these catalysts).1,2 In footnote 13 of reference 1, Brown writes:


  The designations are derived from Purdue University, where this work was initiated.


So, it is within reason to assume that the P stands for Purdue.



References


Brown, C. A. Catalytic hydrogenation. V. Reaction of sodium borohydride with aqueous nickel salts. P-1 nickel boride, a convenient, highly active nickel hydrogenation catalyst. J. Org. Chem. 1970, 35 (6), 1900–1904. DOI: 10.1021/jo00831a039.
Brown, C. A.; Ahuja, V. K. Catalytic hydrogenation. VI. Reaction of sodium borohydride with nickel salts in ethanol solution. P-2 Nickel, a highly convenient, new, selective hydrogenation catalyst with great sensitivity to substrate structure. J. Org. Chem. 1973, 38 (12), 2226–2230. DOI: 10.1021/jo00952a024.